diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index ce38f646..87d933e2 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -124,6 +124,37 @@ jobs:
       - name: Code style with PHP_CodeSniffer
         run: ./vendor/bin/phpcs -q --report=checkstyle | cs2pr
 
+  phpstan:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Setup PHP, with composer and extensions
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: 7.4
+          extensions: ctype, dom, gd, iconv, fileinfo, libxml, mbstring, simplexml, xml, xmlreader, xmlwriter, zip, zlib
+          coverage: none
+          tools: cs2pr
+
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+      - name: Cache composer dependencies
+        uses: actions/cache@v2
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+          restore-keys: ${{ runner.os }}-composer-
+
+      - name: Install dependencies
+        run: composer install --no-progress --prefer-dist --optimize-autoloader
+
+      - name: Static analysis with PHPStan
+        run: ./vendor/bin/phpstan analyse
+
   coverage:
     runs-on: ubuntu-latest
     steps:
diff --git a/composer.json b/composer.json
index 3b4ed556..d0c3a16d 100644
--- a/composer.json
+++ b/composer.json
@@ -41,7 +41,8 @@
         "check": [
             "php-cs-fixer fix --ansi --dry-run --diff",
             "phpcs",
-            "phpunit --color=always"
+            "phpunit --color=always",
+            "phpstan analyse --ansi"
         ],
         "fix": [
             "php-cs-fixer fix --ansi"
@@ -79,6 +80,7 @@
         "jpgraph/jpgraph": "^4.0",
         "mpdf/mpdf": "^8.0",
         "phpcompatibility/php-compatibility": "^9.3",
+        "phpstan/phpstan": "^0.12.82",
         "phpunit/phpunit": "^8.5",
         "squizlabs/php_codesniffer": "^3.5",
         "tecnickcom/tcpdf": "^6.3"
diff --git a/composer.lock b/composer.lock
index 3f6efb00..e4060972 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "6c8f34baf3385a533fade30a9a9ad6f1",
+    "content-hash": "89b62d75519340c289a3a763245f1ca0",
     "packages": [
         {
             "name": "ezyang/htmlpurifier",
@@ -1963,6 +1963,66 @@
             },
             "time": "2021-03-17T13:42:18+00:00"
         },
+        {
+            "name": "phpstan/phpstan",
+            "version": "0.12.82",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/phpstan/phpstan.git",
+                "reference": "3920f0fb0aff39263d3a4cb0bca120a67a1a6a11"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/phpstan/phpstan/zipball/3920f0fb0aff39263d3a4cb0bca120a67a1a6a11",
+                "reference": "3920f0fb0aff39263d3a4cb0bca120a67a1a6a11",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^7.1|^8.0"
+            },
+            "conflict": {
+                "phpstan/phpstan-shim": "*"
+            },
+            "bin": [
+                "phpstan",
+                "phpstan.phar"
+            ],
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "0.12-dev"
+                }
+            },
+            "autoload": {
+                "files": [
+                    "bootstrap.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "description": "PHPStan - PHP Static Analysis Tool",
+            "support": {
+                "issues": "https://github.com/phpstan/phpstan/issues",
+                "source": "https://github.com/phpstan/phpstan/tree/0.12.82"
+            },
+            "funding": [
+                {
+                    "url": "https://github.com/ondrejmirtes",
+                    "type": "github"
+                },
+                {
+                    "url": "https://www.patreon.com/phpstan",
+                    "type": "patreon"
+                },
+                {
+                    "url": "https://tidelift.com/funding/github/packagist/phpstan/phpstan",
+                    "type": "tidelift"
+                }
+            ],
+            "time": "2021-03-19T06:08:17+00:00"
+        },
         {
             "name": "phpunit/php-code-coverage",
             "version": "7.0.14",
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
new file mode 100644
index 00000000..476513dc
--- /dev/null
+++ b/phpstan.neon.dist
@@ -0,0 +1,11 @@
+parameters:
+    level: 1
+    paths:
+        - src/
+        - tests/
+    ignoreErrors:
+        - '~^Class GdImage not found\.$~'
+
+        # Ignore all JpGraph issues
+        - '~^Constant (MARK_CIRCLE|MARK_CROSS|MARK_DIAMOND|MARK_DTRIANGLE|MARK_FILLEDCIRCLE|MARK_SQUARE|MARK_STAR|MARK_UTRIANGLE|MARK_X|SIDE_RIGHT) not found\.$~'
+        - '~^Instantiated class (AccBarPlot|AccLinePlot|BarPlot|ContourPlot|Graph|GroupBarPlot|GroupBarPlot|LinePlot|LinePlot|PieGraph|PiePlot|PiePlot3D|PiePlotC|RadarGraph|RadarPlot|ScatterPlot|Spline|StockPlot) not found\.$~'
diff --git a/src/PhpSpreadsheet/Calculation/Calculation.php b/src/PhpSpreadsheet/Calculation/Calculation.php
index 967d05e5..0aa2a6da 100644
--- a/src/PhpSpreadsheet/Calculation/Calculation.php
+++ b/src/PhpSpreadsheet/Calculation/Calculation.php
@@ -3154,6 +3154,7 @@ class Calculation
                 //    Return Excel errors "as is"
                 return $value;
             }
+
             //    Return strings wrapped in quotes
             return self::FORMULA_STRING_QUOTE . $value . self::FORMULA_STRING_QUOTE;
         } elseif ((is_float($value)) && ((is_nan($value)) || (is_infinite($value)))) {
@@ -3794,13 +3795,13 @@ class Calculation
         $pCellParent = ($pCell !== null) ? $pCell->getWorksheet() : null;
 
         $regexpMatchString = '/^(' . self::CALCULATION_REGEXP_FUNCTION .
-                                '|' . self::CALCULATION_REGEXP_CELLREF .
-                                '|' . self::CALCULATION_REGEXP_NUMBER .
-                                '|' . self::CALCULATION_REGEXP_STRING .
-                                '|' . self::CALCULATION_REGEXP_OPENBRACE .
-                                '|' . self::CALCULATION_REGEXP_DEFINEDNAME .
-                                '|' . self::CALCULATION_REGEXP_ERROR .
-                                ')/sui';
+            '|' . self::CALCULATION_REGEXP_CELLREF .
+            '|' . self::CALCULATION_REGEXP_NUMBER .
+            '|' . self::CALCULATION_REGEXP_STRING .
+            '|' . self::CALCULATION_REGEXP_OPENBRACE .
+            '|' . self::CALCULATION_REGEXP_DEFINEDNAME .
+            '|' . self::CALCULATION_REGEXP_ERROR .
+            ')/sui';
 
         //    Start with initialisation
         $index = 0;
@@ -3939,6 +3940,7 @@ class Calculation
                     }
                     //    Check the argument count
                     $argumentCountError = false;
+                    $expectedArgumentCountString = null;
                     if (is_numeric($expectedArgumentCount)) {
                         if ($expectedArgumentCount < 0) {
                             if ($argumentCount > abs($expectedArgumentCount)) {
@@ -4203,7 +4205,7 @@ class Calculation
                     ((preg_match('/^' . self::CALCULATION_REGEXP_CELLREF . '.*/Ui', substr($formula, $index), $match)) &&
                         ($output[count($output) - 1]['type'] == 'Cell Reference') ||
                         (preg_match('/^' . self::CALCULATION_REGEXP_DEFINEDNAME . '.*/miu', substr($formula, $index), $match)) &&
-                            ($output[count($output) - 1]['type'] == 'Defined Name' || $output[count($output) - 1]['type'] == 'Value')
+                        ($output[count($output) - 1]['type'] == 'Defined Name' || $output[count($output) - 1]['type'] == 'Value')
                     )
                 ) {
                     while (
@@ -4645,6 +4647,9 @@ class Calculation
                     $this->debugLog->writeDebugLog('Evaluating Function ', self::localeFunc($functionName), '() with ', (($argCount == 0) ? 'no' : $argCount), ' argument', (($argCount == 1) ? '' : 's'));
                 }
                 if ((isset(self::$phpSpreadsheetFunctions[$functionName])) || (isset(self::$controlFunctions[$functionName]))) {    // function
+                    $passByReference = false;
+                    $passCellReference = false;
+                    $functionCall = null;
                     if (isset(self::$phpSpreadsheetFunctions[$functionName])) {
                         $functionCall = self::$phpSpreadsheetFunctions[$functionName]['functionCall'];
                         $passByReference = isset(self::$phpSpreadsheetFunctions[$functionName]['passByReference']);
@@ -4945,6 +4950,9 @@ class Calculation
                 }
 
                 break;
+
+            default:
+                throw new Exception('Unsupported binary comparison operation');
         }
 
         //    Log the result details
@@ -5062,6 +5070,9 @@ class Calculation
                         $result = $operand1 ** $operand2;
 
                         break;
+
+                    default:
+                        throw new Exception('Unsupported numeric binary operation');
                 }
             }
         }
diff --git a/src/PhpSpreadsheet/Calculation/DateTime.php b/src/PhpSpreadsheet/Calculation/DateTime.php
index 744d9589..e3580cde 100644
--- a/src/PhpSpreadsheet/Calculation/DateTime.php
+++ b/src/PhpSpreadsheet/Calculation/DateTime.php
@@ -651,7 +651,7 @@ class DateTime
      *
      * Returns the ISO 8601 week number of the year for a specified date.
      *
-     * @Deprecated 2.0.0 Use the funcIsoWeeknum method in the DateTimeExcel\Isoweeknum class instead
+     * @Deprecated 2.0.0 Use the funcIsoWeeknum method in the DateTimeExcel\IsoWeekNum class instead
      *
      * Excel Function:
      *        ISOWEEKNUM(dateValue)
@@ -663,7 +663,7 @@ class DateTime
      */
     public static function ISOWEEKNUM($dateValue = 1)
     {
-        return DateTimeExcel\IsoweekNum::funcIsoWeekNum($dateValue);
+        return DateTimeExcel\IsoWeekNum::funcIsoWeekNum($dateValue);
     }
 
     /**
diff --git a/src/PhpSpreadsheet/Calculation/Financial.php b/src/PhpSpreadsheet/Calculation/Financial.php
index 11bbf7a6..547ad6b3 100644
--- a/src/PhpSpreadsheet/Calculation/Financial.php
+++ b/src/PhpSpreadsheet/Calculation/Financial.php
@@ -20,6 +20,8 @@ class Financial
     {
         $pmt = self::PMT($rate, $nper, $pv, $fv, $type);
         $capital = $pv;
+        $interest = 0;
+        $principal = 0;
         for ($i = 1; $i <= $per; ++$i) {
             $interest = ($type && $i == 1) ? 0 : -$capital * $rate;
             $principal = $pmt - $interest;
diff --git a/src/PhpSpreadsheet/Chart/Renderer/JpGraph.php b/src/PhpSpreadsheet/Chart/Renderer/JpGraph.php
index 02fbfed7..0ab70870 100644
--- a/src/PhpSpreadsheet/Chart/Renderer/JpGraph.php
+++ b/src/PhpSpreadsheet/Chart/Renderer/JpGraph.php
@@ -301,6 +301,8 @@ class JpGraph implements IRenderer
         $seriesPlots = [];
         if ($grouping == 'percentStacked') {
             $sumValues = $this->percentageSumCalculation($groupID, $seriesCount);
+        } else {
+            $sumValues = [];
         }
 
         //    Loop through each data series in turn
@@ -376,6 +378,8 @@ class JpGraph implements IRenderer
         $seriesPlots = [];
         if ($grouping == 'percentStacked') {
             $sumValues = $this->percentageSumCalculation($groupID, $seriesCount);
+        } else {
+            $sumValues = [];
         }
 
         //    Loop through each data series in turn
diff --git a/src/PhpSpreadsheet/IOFactory.php b/src/PhpSpreadsheet/IOFactory.php
index ab04e969..06006edc 100644
--- a/src/PhpSpreadsheet/IOFactory.php
+++ b/src/PhpSpreadsheet/IOFactory.php
@@ -120,7 +120,7 @@ abstract class IOFactory
             $reader = self::createReader($guessedReader);
 
             // Let's see if we are lucky
-            if (isset($reader) && $reader->canRead($filename)) {
+            if ($reader->canRead($filename)) {
                 return $reader;
             }
         }
diff --git a/src/PhpSpreadsheet/Reader/Xls.php b/src/PhpSpreadsheet/Reader/Xls.php
index 6d6b87fd..faa047da 100644
--- a/src/PhpSpreadsheet/Reader/Xls.php
+++ b/src/PhpSpreadsheet/Reader/Xls.php
@@ -801,9 +801,10 @@ class Xls extends BaseReader
         }
 
         // treat MSODRAWINGGROUP records, workbook-level Escher
+        $escherWorkbook = null;
         if (!$this->readDataOnly && $this->drawingGroupData) {
-            $escherWorkbook = new Escher();
-            $reader = new Xls\Escher($escherWorkbook);
+            $escher = new Escher();
+            $reader = new Xls\Escher($escher);
             $escherWorkbook = $reader->load($this->drawingGroupData);
         }
 
@@ -1133,38 +1134,40 @@ class Xls extends BaseReader
                                 continue 2;
                             }
 
-                            $BSECollection = $escherWorkbook->getDggContainer()->getBstoreContainer()->getBSECollection();
-                            $BSE = $BSECollection[$BSEindex - 1];
-                            $blipType = $BSE->getBlipType();
+                            if ($escherWorkbook) {
+                                $BSECollection = $escherWorkbook->getDggContainer()->getBstoreContainer()->getBSECollection();
+                                $BSE = $BSECollection[$BSEindex - 1];
+                                $blipType = $BSE->getBlipType();
 
-                            // need check because some blip types are not supported by Escher reader such as EMF
-                            if ($blip = $BSE->getBlip()) {
-                                $ih = imagecreatefromstring($blip->getData());
-                                $drawing = new MemoryDrawing();
-                                $drawing->setImageResource($ih);
+                                // need check because some blip types are not supported by Escher reader such as EMF
+                                if ($blip = $BSE->getBlip()) {
+                                    $ih = imagecreatefromstring($blip->getData());
+                                    $drawing = new MemoryDrawing();
+                                    $drawing->setImageResource($ih);
 
-                                // width, height, offsetX, offsetY
-                                $drawing->setResizeProportional(false);
-                                $drawing->setWidth($width);
-                                $drawing->setHeight($height);
-                                $drawing->setOffsetX($offsetX);
-                                $drawing->setOffsetY($offsetY);
+                                    // width, height, offsetX, offsetY
+                                    $drawing->setResizeProportional(false);
+                                    $drawing->setWidth($width);
+                                    $drawing->setHeight($height);
+                                    $drawing->setOffsetX($offsetX);
+                                    $drawing->setOffsetY($offsetY);
 
-                                switch ($blipType) {
-                                    case BSE::BLIPTYPE_JPEG:
-                                        $drawing->setRenderingFunction(MemoryDrawing::RENDERING_JPEG);
-                                        $drawing->setMimeType(MemoryDrawing::MIMETYPE_JPEG);
+                                    switch ($blipType) {
+                                        case BSE::BLIPTYPE_JPEG:
+                                            $drawing->setRenderingFunction(MemoryDrawing::RENDERING_JPEG);
+                                            $drawing->setMimeType(MemoryDrawing::MIMETYPE_JPEG);
 
-                                        break;
-                                    case BSE::BLIPTYPE_PNG:
-                                        $drawing->setRenderingFunction(MemoryDrawing::RENDERING_PNG);
-                                        $drawing->setMimeType(MemoryDrawing::MIMETYPE_PNG);
+                                            break;
+                                        case BSE::BLIPTYPE_PNG:
+                                            $drawing->setRenderingFunction(MemoryDrawing::RENDERING_PNG);
+                                            $drawing->setMimeType(MemoryDrawing::MIMETYPE_PNG);
 
-                                        break;
+                                            break;
+                                    }
+
+                                    $drawing->setWorksheet($this->phpSheet);
+                                    $drawing->setCoordinates($spContainer->getStartCoordinates());
                                 }
-
-                                $drawing->setWorksheet($this->phpSheet);
-                                $drawing->setCoordinates($spContainer->getStartCoordinates());
                             }
 
                             break;
@@ -2742,6 +2745,7 @@ class Xls extends BaseReader
         $sheetType = ord($recordData[5]);
 
         // offset: 6; size: var; sheet name
+        $rec_name = null;
         if ($this->version == self::XLS_BIFF8) {
             $string = self::readUnicodeStringShort(substr($recordData, 6));
             $rec_name = $string['value'];
@@ -3018,12 +3022,14 @@ class Xls extends BaseReader
             // bit: 3; mask: 0x03; 0 = ordinary; 1 = Rich-Text
             $hasRichText = (($optionFlags & 0x08) != 0);
 
+            $formattingRuns = 0;
             if ($hasRichText) {
                 // number of Rich-Text formatting runs
                 $formattingRuns = self::getUInt2d($recordData, $pos);
                 $pos += 2;
             }
 
+            $extendedRunLength = 0;
             if ($hasAsian) {
                 // size of Asian phonetic setting
                 $extendedRunLength = self::getInt4d($recordData, $pos);
@@ -3034,6 +3040,7 @@ class Xls extends BaseReader
             $len = ($isCompressed) ? $numChars : $numChars * 2;
 
             // look up limit position - Check it again to be sure that no error occurs when parsing SST structure
+            $limitpos = null;
             foreach ($spliceOffsets as $spliceOffset) {
                 // it can happen that the string is empty, therefore we need
                 // <= and not just <
@@ -4385,6 +4392,8 @@ class Xls extends BaseReader
 
         // offset: 4; size: 2; index to first visible colum
         $firstVisibleColumn = self::getUInt2d($recordData, 4);
+        $zoomscaleInPageBreakPreview = 0;
+        $zoomscaleInNormalView = 0;
         if ($this->version === self::XLS_BIFF8) {
             // offset:  8; size: 2; not used
             // offset: 10; size: 2; cached magnification factor in page break preview (in percent); 0 = Default (60%)
@@ -7636,6 +7645,8 @@ class Xls extends BaseReader
                 $size = 9;
 
                 break;
+            default:
+                throw new PhpSpreadsheetException('Unsupported BIFF8 constant');
         }
 
         return [
diff --git a/src/PhpSpreadsheet/Reader/Xls/Color.php b/src/PhpSpreadsheet/Reader/Xls/Color.php
index c45f88c7..06c2d0b9 100644
--- a/src/PhpSpreadsheet/Reader/Xls/Color.php
+++ b/src/PhpSpreadsheet/Reader/Xls/Color.php
@@ -20,7 +20,7 @@ class Color
         if ($color <= 0x07 || $color >= 0x40) {
             // special built-in color
             return Color\BuiltIn::lookup($color);
-        } elseif (isset($palette, $palette[$color - 8])) {
+        } elseif (isset($palette[$color - 8])) {
             // palette color, color index 0x08 maps to pallete index 0
             return $palette[$color - 8];
         }
diff --git a/src/PhpSpreadsheet/Reader/Xlsx.php b/src/PhpSpreadsheet/Reader/Xlsx.php
index 219a49fb..e47ad7b0 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx.php
@@ -430,7 +430,7 @@ class Xlsx extends BaseReader
                             'SimpleXMLElement',
                             Settings::getLibXmlLoaderOptions()
                         );
-                        if (isset($xmlStrings, $xmlStrings->si)) {
+                        if (isset($xmlStrings->si)) {
                             foreach ($xmlStrings->si as $val) {
                                 if (isset($val->t)) {
                                     $sharedStrings[] = StringHelper::controlCharacterOOXML2PHP((string) $val->t);
@@ -511,10 +511,7 @@ class Xlsx extends BaseReader
                                     $numFmt = NumberFormat::builtInFormatCode((int) $xf['numFmtId']);
                                 }
                             }
-                            $quotePrefix = false;
-                            if (isset($xf['quotePrefix'])) {
-                                $quotePrefix = (bool) $xf['quotePrefix'];
-                            }
+                            $quotePrefix = (bool) ($xf['quotePrefix'] ?? false);
 
                             $style = (object) [
                                 'numFmt' => $numFmt ?? NumberFormat::FORMAT_GENERAL,
@@ -544,6 +541,8 @@ class Xlsx extends BaseReader
                                 }
                             }
 
+                            $quotePrefix = (bool) ($xf['quotePrefix'] ?? false);
+
                             $cellStyle = (object) [
                                 'numFmt' => $numFmt,
                                 'font' => $xmlStyles->fonts->font[(int) ($xf['fontId'])],
@@ -1081,6 +1080,7 @@ class Xlsx extends BaseReader
                                 }
                                 if ($xmlSheet->drawing && !$this->readDataOnly) {
                                     $unparsedDrawings = [];
+                                    $fileDrawing = null;
                                     foreach ($xmlSheet->drawing as $drawing) {
                                         $drawingRelId = (string) self::getArrayItem($drawing->attributes('http://schemas.openxmlformats.org/officeDocument/2006/relationships'), 'id');
                                         $fileDrawing = $drawings[$drawingRelId];
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/Chart.php b/src/PhpSpreadsheet/Reader/Xlsx/Chart.php
index 5a3439f2..5e86c60a 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/Chart.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/Chart.php
@@ -61,7 +61,7 @@ class Chart
 
         $XaxisLabel = $YaxisLabel = $legend = $title = null;
         $dispBlanksAs = $plotVisOnly = null;
-
+        $plotArea = null;
         foreach ($chartElementsC as $chartElementKey => $chartElement) {
             switch ($chartElementKey) {
                 case 'chart':
diff --git a/src/PhpSpreadsheet/Reader/Xml.php b/src/PhpSpreadsheet/Reader/Xml.php
index a827d17a..58d38b0d 100644
--- a/src/PhpSpreadsheet/Reader/Xml.php
+++ b/src/PhpSpreadsheet/Reader/Xml.php
@@ -436,6 +436,7 @@ class Xml extends BaseReader
             // Create new Worksheet
             $spreadsheet->createSheet();
             $spreadsheet->setActiveSheetIndex($worksheetID);
+            $worksheetName = '';
             if (isset($worksheet_ss['Name'])) {
                 $worksheetName = (string) $worksheet_ss['Name'];
                 //    Use false for $updateFormulaCellReferences to prevent adjustment of worksheet references in
diff --git a/src/PhpSpreadsheet/Shared/Drawing.php b/src/PhpSpreadsheet/Shared/Drawing.php
index f41fb695..67c015c4 100644
--- a/src/PhpSpreadsheet/Shared/Drawing.php
+++ b/src/PhpSpreadsheet/Shared/Drawing.php
@@ -171,6 +171,8 @@ class Drawing
 
         //    Process the header
         //    Structure: http://www.fastgraph.com/help/bmp_header_format.html
+        $width = 0;
+        $height = 0;
         if (substr($header, 0, 4) == '424d') {
             //    Cut it in parts of 2 bytes
             $header_parts = str_split($header, 2);
diff --git a/src/PhpSpreadsheet/Shared/Font.php b/src/PhpSpreadsheet/Shared/Font.php
index 162e9730..4061b370 100644
--- a/src/PhpSpreadsheet/Shared/Font.php
+++ b/src/PhpSpreadsheet/Shared/Font.php
@@ -244,6 +244,7 @@ class Font
 
         // Try to get the exact text width in pixels
         $approximate = self::$autoSizeMethod == self::AUTOSIZE_METHOD_APPROX;
+        $columnWidth = 0;
         if (!$approximate) {
             $columnWidthAdjust = ceil(self::getTextWidthPixelsExact('n', $font, 0) * 1.07);
 
diff --git a/src/PhpSpreadsheet/Shared/JAMA/EigenvalueDecomposition.php b/src/PhpSpreadsheet/Shared/JAMA/EigenvalueDecomposition.php
index 4c67c3a9..5c6ccfd3 100644
--- a/src/PhpSpreadsheet/Shared/JAMA/EigenvalueDecomposition.php
+++ b/src/PhpSpreadsheet/Shared/JAMA/EigenvalueDecomposition.php
@@ -18,9 +18,9 @@ namespace PhpOffice\PhpSpreadsheet\Shared\JAMA;
  *    conditioned, or even singular, so the validity of the equation
  *    A = V*D*inverse(V) depends upon V.cond().
  *
- *    @author  Paul Meagher
+ * @author  Paul Meagher
  *
- *    @version 1.1
+ * @version 1.1
  */
 class EigenvalueDecomposition
 {
@@ -70,6 +70,11 @@ class EigenvalueDecomposition
 
     private $cdivi;
 
+    /**
+     * @var array
+     */
+    private $A;
+
     /**
      * Symmetric Householder reduction to tridiagonal form.
      */
@@ -80,6 +85,7 @@ class EigenvalueDecomposition
         //  Auto. Comp., Vol.ii-Linear Algebra, and the corresponding
         //  Fortran subroutine in EISPACK.
         $this->d = $this->V[$this->n - 1];
+        $j = 0;
         // Householder reduction to tridiagonal form.
         for ($i = $this->n - 1; $i > 0; --$i) {
             $i_ = $i - 1;
@@ -781,9 +787,9 @@ class EigenvalueDecomposition
     /**
      * Constructor: Check for symmetry, then construct the eigenvalue decomposition.
      *
-     * @param mixed $Arg A Square matrix
+     * @param Matrix $Arg A Square matrix
      */
-    public function __construct($Arg)
+    public function __construct(Matrix $Arg)
     {
         $this->A = $Arg->getArray();
         $this->n = $Arg->getColumnDimension();
@@ -848,6 +854,7 @@ class EigenvalueDecomposition
      */
     public function getD()
     {
+        $D = [];
         for ($i = 0; $i < $this->n; ++$i) {
             $D[$i] = array_fill(0, $this->n, 0.0);
             $D[$i][$i] = $this->d[$i];
diff --git a/src/PhpSpreadsheet/Shared/JAMA/LUDecomposition.php b/src/PhpSpreadsheet/Shared/JAMA/LUDecomposition.php
index 6db17c28..e16d6a21 100644
--- a/src/PhpSpreadsheet/Shared/JAMA/LUDecomposition.php
+++ b/src/PhpSpreadsheet/Shared/JAMA/LUDecomposition.php
@@ -135,6 +135,7 @@ class LUDecomposition
      */
     public function getL()
     {
+        $L = [];
         for ($i = 0; $i < $this->m; ++$i) {
             for ($j = 0; $j < $this->n; ++$j) {
                 if ($i > $j) {
@@ -159,6 +160,7 @@ class LUDecomposition
      */
     public function getU()
     {
+        $U = [];
         for ($i = 0; $i < $this->n; ++$i) {
             for ($j = 0; $j < $this->n; ++$j) {
                 if ($i <= $j) {
diff --git a/src/PhpSpreadsheet/Shared/JAMA/SingularValueDecomposition.php b/src/PhpSpreadsheet/Shared/JAMA/SingularValueDecomposition.php
index b997fb7c..afd9ed0f 100644
--- a/src/PhpSpreadsheet/Shared/JAMA/SingularValueDecomposition.php
+++ b/src/PhpSpreadsheet/Shared/JAMA/SingularValueDecomposition.php
@@ -476,6 +476,7 @@ class SingularValueDecomposition
      */
     public function getS()
     {
+        $S = [];
         for ($i = 0; $i < $this->n; ++$i) {
             for ($j = 0; $j < $this->n; ++$j) {
                 $S[$i][$j] = 0.0;
diff --git a/src/PhpSpreadsheet/Shared/OLE.php b/src/PhpSpreadsheet/Shared/OLE.php
index 1c745bdb..f65fbca7 100644
--- a/src/PhpSpreadsheet/Shared/OLE.php
+++ b/src/PhpSpreadsheet/Shared/OLE.php
@@ -21,6 +21,7 @@ namespace PhpOffice\PhpSpreadsheet\Shared;
 // +----------------------------------------------------------------------+
 //
 
+use PhpOffice\PhpSpreadsheet\Exception;
 use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
 use PhpOffice\PhpSpreadsheet\Shared\OLE\ChainedBlockStream;
 use PhpOffice\PhpSpreadsheet\Shared\OLE\PPS\Root;
@@ -317,7 +318,7 @@ class OLE
 
                     break;
                 default:
-                    break;
+                    throw new Exception('Unsupported PPS type');
             }
             fseek($fh, 1, SEEK_CUR);
             $pps->Type = $type;
@@ -496,7 +497,7 @@ class OLE
      */
     public static function localDateToOLE($date)
     {
-        if (!isset($date)) {
+        if (!$date) {
             return "\x00\x00\x00\x00\x00\x00\x00\x00";
         }
 
diff --git a/src/PhpSpreadsheet/Shared/Trend/Trend.php b/src/PhpSpreadsheet/Shared/Trend/Trend.php
index d0a117cb..24570d59 100644
--- a/src/PhpSpreadsheet/Shared/Trend/Trend.php
+++ b/src/PhpSpreadsheet/Shared/Trend/Trend.php
@@ -91,6 +91,8 @@ class Trend
             case self::TREND_BEST_FIT_NO_POLY:
                 //    If the request is to determine the best fit regression, then we test each Trend line in turn
                 //    Start by generating an instance of each available Trend method
+                $bestFit = [];
+                $bestFitValue = [];
                 foreach (self::$trendTypes as $trendMethod) {
                     $className = '\PhpOffice\PhpSpreadsheet\Shared\Trend\\' . $trendType . 'BestFit';
                     $bestFit[$trendMethod] = new $className($yValues, $xValues, $const);
diff --git a/src/PhpSpreadsheet/Spreadsheet.php b/src/PhpSpreadsheet/Spreadsheet.php
index 51f558a1..59304804 100644
--- a/src/PhpSpreadsheet/Spreadsheet.php
+++ b/src/PhpSpreadsheet/Spreadsheet.php
@@ -55,7 +55,7 @@ class Spreadsheet
     /**
      * Calculation Engine.
      *
-     * @var Calculation
+     * @var null|Calculation
      */
     private $calculationEngine;
 
@@ -505,8 +505,8 @@ class Spreadsheet
      */
     public function __destruct()
     {
-        $this->calculationEngine = null;
         $this->disconnectWorksheets();
+        $this->calculationEngine = null;
     }
 
     /**
@@ -527,7 +527,7 @@ class Spreadsheet
     /**
      * Return the calculation engine for this worksheet.
      *
-     * @return Calculation
+     * @return null|Calculation
      */
     public function getCalculationEngine()
     {
@@ -1343,6 +1343,7 @@ class Spreadsheet
         // remove cellXfs without references and create mapping so we can update xfIndex
         // for all cells and columns
         $countNeededCellXfs = 0;
+        $map = [];
         foreach ($this->cellXfCollection as $index => $cellXf) {
             if ($countReferencesCellXf[$index] > 0 || $index == 0) { // we must never remove the first cellXf
                 ++$countNeededCellXfs;
diff --git a/src/PhpSpreadsheet/Style/Border.php b/src/PhpSpreadsheet/Style/Border.php
index 1d3096f0..d11fa0ca 100644
--- a/src/PhpSpreadsheet/Style/Border.php
+++ b/src/PhpSpreadsheet/Style/Border.php
@@ -47,11 +47,8 @@ class Border extends Supervisor
      * @param bool $isSupervisor Flag indicating if this is a supervisor or not
      *                                    Leave this value at default unless you understand exactly what
      *                                        its ramifications are
-     * @param bool $isConditional Flag indicating if this is a conditional style or not
-     *                                    Leave this value at default unless you understand exactly what
-     *                                        its ramifications are
      */
-    public function __construct($isSupervisor = false, $isConditional = false)
+    public function __construct($isSupervisor = false)
     {
         // Supervisor?
         parent::__construct($isSupervisor);
diff --git a/src/PhpSpreadsheet/Style/Borders.php b/src/PhpSpreadsheet/Style/Borders.php
index a1acfdd4..eeb4932a 100644
--- a/src/PhpSpreadsheet/Style/Borders.php
+++ b/src/PhpSpreadsheet/Style/Borders.php
@@ -95,21 +95,18 @@ class Borders extends Supervisor
      * @param bool $isSupervisor Flag indicating if this is a supervisor or not
      *                                    Leave this value at default unless you understand exactly what
      *                                        its ramifications are
-     * @param bool $isConditional Flag indicating if this is a conditional style or not
-     *                                    Leave this value at default unless you understand exactly what
-     *                                        its ramifications are
      */
-    public function __construct($isSupervisor = false, $isConditional = false)
+    public function __construct($isSupervisor = false)
     {
         // Supervisor?
         parent::__construct($isSupervisor);
 
         // Initialise values
-        $this->left = new Border($isSupervisor, $isConditional);
-        $this->right = new Border($isSupervisor, $isConditional);
-        $this->top = new Border($isSupervisor, $isConditional);
-        $this->bottom = new Border($isSupervisor, $isConditional);
-        $this->diagonal = new Border($isSupervisor, $isConditional);
+        $this->left = new Border($isSupervisor);
+        $this->right = new Border($isSupervisor);
+        $this->top = new Border($isSupervisor);
+        $this->bottom = new Border($isSupervisor);
+        $this->diagonal = new Border($isSupervisor);
         $this->diagonalDirection = self::DIAGONAL_NONE;
 
         // Specially for supervisor
diff --git a/src/PhpSpreadsheet/Style/NumberFormat/NumberFormatter.php b/src/PhpSpreadsheet/Style/NumberFormat/NumberFormatter.php
index 36cdcf03..9a4f32ac 100644
--- a/src/PhpSpreadsheet/Style/NumberFormat/NumberFormatter.php
+++ b/src/PhpSpreadsheet/Style/NumberFormat/NumberFormatter.php
@@ -35,6 +35,7 @@ class NumberFormatter
         if ($maskingBlockCount > 1) {
             $maskingBlocks = array_reverse($maskingBlocks[0]);
 
+            $offset = 0;
             foreach ($maskingBlocks as $block) {
                 $size = strlen($block[0]);
                 $divisor = 10 ** $size;
diff --git a/src/PhpSpreadsheet/Style/Style.php b/src/PhpSpreadsheet/Style/Style.php
index 7fec9a00..d3653ed5 100644
--- a/src/PhpSpreadsheet/Style/Style.php
+++ b/src/PhpSpreadsheet/Style/Style.php
@@ -80,7 +80,7 @@ class Style extends Supervisor
         // Initialise values
         $this->font = new Font($isSupervisor, $isConditional);
         $this->fill = new Fill($isSupervisor, $isConditional);
-        $this->borders = new Borders($isSupervisor, $isConditional);
+        $this->borders = new Borders($isSupervisor);
         $this->alignment = new Alignment($isSupervisor, $isConditional);
         $this->numberFormat = new NumberFormat($isSupervisor, $isConditional);
         $this->protection = new Protection($isSupervisor, $isConditional);
@@ -257,11 +257,11 @@ class Style extends Supervisor
                     // start column index for region
                     $colStart = ($x == 3) ?
                         Coordinate::stringFromColumnIndex($rangeEnd[0])
-                            : Coordinate::stringFromColumnIndex($rangeStart[0] + $x - 1);
+                        : Coordinate::stringFromColumnIndex($rangeStart[0] + $x - 1);
                     // end column index for region
                     $colEnd = ($x == 1) ?
                         Coordinate::stringFromColumnIndex($rangeStart[0])
-                            : Coordinate::stringFromColumnIndex($rangeEnd[0] - $xMax + $x);
+                        : Coordinate::stringFromColumnIndex($rangeEnd[0] - $xMax + $x);
 
                     for ($y = 1; $y <= $yMax; ++$y) {
                         // which edges are touching the region
@@ -349,56 +349,11 @@ class Style extends Supervisor
             }
 
             // First loop through columns, rows, or cells to find out which styles are affected by this operation
-            switch ($selectionType) {
-                case 'COLUMN':
-                    $oldXfIndexes = [];
-                    for ($col = $rangeStart[0]; $col <= $rangeEnd[0]; ++$col) {
-                        $oldXfIndexes[$this->getActiveSheet()->getColumnDimensionByColumn($col)->getXfIndex()] = true;
-                    }
-                    foreach ($this->getActiveSheet()->getColumnIterator($rangeStart0, $rangeEnd0) as $columnIterator) {
-                        $cellIterator = $columnIterator->getCellIterator();
-                        $cellIterator->setIterateOnlyExistingCells(true);
-                        foreach ($cellIterator as $columnCell) {
-                            if ($columnCell !== null) {
-                                $columnCell->getStyle()->applyFromArray($pStyles);
-                            }
-                        }
-                    }
-
-                    break;
-                case 'ROW':
-                    $oldXfIndexes = [];
-                    for ($row = $rangeStart[1]; $row <= $rangeEnd[1]; ++$row) {
-                        if ($this->getActiveSheet()->getRowDimension($row)->getXfIndex() === null) {
-                            $oldXfIndexes[0] = true; // row without explicit style should be formatted based on default style
-                        } else {
-                            $oldXfIndexes[$this->getActiveSheet()->getRowDimension($row)->getXfIndex()] = true;
-                        }
-                    }
-                    foreach ($this->getActiveSheet()->getRowIterator((int) $rangeStart[1], (int) $rangeEnd[1]) as $rowIterator) {
-                        $cellIterator = $rowIterator->getCellIterator();
-                        $cellIterator->setIterateOnlyExistingCells(true);
-                        foreach ($cellIterator as $rowCell) {
-                            if ($rowCell !== null) {
-                                $rowCell->getStyle()->applyFromArray($pStyles);
-                            }
-                        }
-                    }
-
-                    break;
-                case 'CELL':
-                    $oldXfIndexes = [];
-                    for ($col = $rangeStart[0]; $col <= $rangeEnd[0]; ++$col) {
-                        for ($row = $rangeStart[1]; $row <= $rangeEnd[1]; ++$row) {
-                            $oldXfIndexes[$this->getActiveSheet()->getCellByColumnAndRow($col, $row)->getXfIndex()] = true;
-                        }
-                    }
-
-                    break;
-            }
+            $oldXfIndexes = $this->getOldXfIndexes($selectionType, $rangeStart, $rangeEnd, $rangeStart0, $rangeEnd0, $pStyles);
 
             // clone each of the affected styles, apply the style array, and add the new styles to the workbook
             $workbook = $this->getActiveSheet()->getParent();
+            $newXfIndexes = [];
             foreach ($oldXfIndexes as $oldXfIndex => $dummy) {
                 $style = $workbook->getCellXfByIndex($oldXfIndex);
                 $newStyle = clone $style;
@@ -472,6 +427,57 @@ class Style extends Supervisor
         return $this;
     }
 
+    private function getOldXfIndexes(string $selectionType, array $rangeStart, array $rangeEnd, string $rangeStart0, string $rangeEnd0, array $pStyles): array
+    {
+        $oldXfIndexes = [];
+        switch ($selectionType) {
+            case 'COLUMN':
+                for ($col = $rangeStart[0]; $col <= $rangeEnd[0]; ++$col) {
+                    $oldXfIndexes[$this->getActiveSheet()->getColumnDimensionByColumn($col)->getXfIndex()] = true;
+                }
+                foreach ($this->getActiveSheet()->getColumnIterator($rangeStart0, $rangeEnd0) as $columnIterator) {
+                    $cellIterator = $columnIterator->getCellIterator();
+                    $cellIterator->setIterateOnlyExistingCells(true);
+                    foreach ($cellIterator as $columnCell) {
+                        if ($columnCell !== null) {
+                            $columnCell->getStyle()->applyFromArray($pStyles);
+                        }
+                    }
+                }
+
+                break;
+            case 'ROW':
+                for ($row = $rangeStart[1]; $row <= $rangeEnd[1]; ++$row) {
+                    if ($this->getActiveSheet()->getRowDimension($row)->getXfIndex() === null) {
+                        $oldXfIndexes[0] = true; // row without explicit style should be formatted based on default style
+                    } else {
+                        $oldXfIndexes[$this->getActiveSheet()->getRowDimension($row)->getXfIndex()] = true;
+                    }
+                }
+                foreach ($this->getActiveSheet()->getRowIterator((int) $rangeStart[1], (int) $rangeEnd[1]) as $rowIterator) {
+                    $cellIterator = $rowIterator->getCellIterator();
+                    $cellIterator->setIterateOnlyExistingCells(true);
+                    foreach ($cellIterator as $rowCell) {
+                        if ($rowCell !== null) {
+                            $rowCell->getStyle()->applyFromArray($pStyles);
+                        }
+                    }
+                }
+
+                break;
+            case 'CELL':
+                for ($col = $rangeStart[0]; $col <= $rangeEnd[0]; ++$col) {
+                    for ($row = $rangeStart[1]; $row <= $rangeEnd[1]; ++$row) {
+                        $oldXfIndexes[$this->getActiveSheet()->getCellByColumnAndRow($col, $row)->getXfIndex()] = true;
+                    }
+                }
+
+                break;
+        }
+
+        return $oldXfIndexes;
+    }
+
     /**
      * Get Fill.
      *
diff --git a/src/PhpSpreadsheet/Worksheet/AutoFilter.php b/src/PhpSpreadsheet/Worksheet/AutoFilter.php
index 22fc775c..dc876ee9 100644
--- a/src/PhpSpreadsheet/Worksheet/AutoFilter.php
+++ b/src/PhpSpreadsheet/Worksheet/AutoFilter.php
@@ -779,6 +779,9 @@ class AutoFilter
                 case AutoFilter\Column::AUTOFILTER_FILTERTYPE_TOPTENFILTER:
                     $ruleValues = [];
                     $dataRowCount = $rangeEnd[1] - $rangeStart[1];
+                    $toptenRuleType = null;
+                    $ruleValue = null;
+                    $ruleOperator = null;
                     foreach ($rules as $rule) {
                         //    We should only ever have one Dynamic Filter Rule anyway
                         $toptenRuleType = $rule->getGrouping();
diff --git a/src/PhpSpreadsheet/Writer/Xls.php b/src/PhpSpreadsheet/Writer/Xls.php
index c7c2e7d6..d458fc74 100644
--- a/src/PhpSpreadsheet/Writer/Xls.php
+++ b/src/PhpSpreadsheet/Writer/Xls.php
@@ -420,6 +420,7 @@ class Xls extends BaseWriter
 
     private function processDrawing(BstoreContainer &$bstoreContainer, BaseDrawing $drawing): void
     {
+        $blipType = null;
         $blipData = '';
         $filename = $drawing->getPath();
 
diff --git a/src/PhpSpreadsheet/Writer/Xls/Parser.php b/src/PhpSpreadsheet/Writer/Xls/Parser.php
index f89957a4..98b2b5cc 100644
--- a/src/PhpSpreadsheet/Writer/Xls/Parser.php
+++ b/src/PhpSpreadsheet/Writer/Xls/Parser.php
@@ -747,7 +747,7 @@ class Parser
         return pack('C', 0xFF);
     }
 
-    private function convertDefinedName(string $name): void
+    private function convertDefinedName(string $name): string
     {
         if (strlen($name) > 255) {
             throw new WriterException('Defined Name is too long');
@@ -764,7 +764,8 @@ class Parser
         $ptgRef = pack('Cvxx', $this->ptg['ptgName'], $nameReference);
 
         throw new WriterException('Cannot yet write formulae with defined names to Xls');
-//        return $ptgRef;
+
+        return $ptgRef;
     }
 
     /**
@@ -968,6 +969,7 @@ class Parser
      */
     private function advance()
     {
+        $token = '';
         $i = $this->currentCharacter;
         $formula_length = strlen($this->formula);
         // eat up white spaces
diff --git a/src/PhpSpreadsheet/Writer/Xls/Worksheet.php b/src/PhpSpreadsheet/Writer/Xls/Worksheet.php
index d2784d6d..8f6015de 100644
--- a/src/PhpSpreadsheet/Writer/Xls/Worksheet.php
+++ b/src/PhpSpreadsheet/Writer/Xls/Worksheet.php
@@ -1344,32 +1344,13 @@ class Worksheet extends BIFFwriter
      */
     private function writeColinfo($col_array): void
     {
-        if (isset($col_array[0])) {
-            $colFirst = $col_array[0];
-        }
-        if (isset($col_array[1])) {
-            $colLast = $col_array[1];
-        }
-        if (isset($col_array[2])) {
-            $coldx = $col_array[2];
-        } else {
-            $coldx = 8.43;
-        }
-        if (isset($col_array[3])) {
-            $xfIndex = $col_array[3];
-        } else {
-            $xfIndex = 15;
-        }
-        if (isset($col_array[4])) {
-            $grbit = $col_array[4];
-        } else {
-            $grbit = 0;
-        }
-        if (isset($col_array[5])) {
-            $level = $col_array[5];
-        } else {
-            $level = 0;
-        }
+        $colFirst = $col_array[0] ?? null;
+        $colLast = $col_array[1] ?? null;
+        $coldx = $col_array[2] ?? 8.43;
+        $xfIndex = $col_array[3] ?? 15;
+        $grbit = $col_array[4] ?? 0;
+        $level = $col_array[5] ?? 0;
+
         $record = 0x007D; // Record identifier
         $length = 0x000C; // Number of bytes to follow
 
@@ -1425,13 +1406,6 @@ class Worksheet extends BIFFwriter
         $irefAct = 0; // Active cell ref
         $cref = 1; // Number of refs
 
-        if (!isset($rwLast)) {
-            $rwLast = $rwFirst; // Last  row in reference
-        }
-        if (!isset($colLast)) {
-            $colLast = $colFirst; // Last  col in reference
-        }
-
         // Swap last row/col for first row/col as necessary
         if ($rwFirst > $rwLast) {
             [$rwFirst, $rwLast] = [$rwLast, $rwFirst];
@@ -1660,7 +1634,7 @@ class Worksheet extends BIFFwriter
             if (!isset($rwTop)) {
                 $rwTop = $y;
             }
-            if (!isset($colLeft)) {
+            if (!$colLeft) {
                 $colLeft = $x;
             }
         } else {
@@ -1668,7 +1642,7 @@ class Worksheet extends BIFFwriter
             if (!isset($rwTop)) {
                 $rwTop = 0;
             }
-            if (!isset($colLeft)) {
+            if (!$colLeft) {
                 $colLeft = 0;
             }
 
@@ -1684,7 +1658,7 @@ class Worksheet extends BIFFwriter
         // Determine which pane should be active. There is also the undocumented
         // option to override this should it be necessary: may be removed later.
         //
-        if (!isset($pnnAct)) {
+        if (!$pnnAct) {
             if ($x != 0 && $y != 0) {
                 $pnnAct = 0; // Bottom right
             }
@@ -2974,9 +2948,9 @@ class Worksheet extends BIFFwriter
     private function writeCFRule(Conditional $conditional): void
     {
         $record = 0x01B1; // Record identifier
+        $type = null;  //  Type of the CF
+        $operatorType = null;   //  Comparison operator
 
-        // $type : Type of the CF
-        // $operatorType : Comparison operator
         if ($conditional->getConditionType() == Conditional::CONDITION_EXPRESSION) {
             $type = 0x02;
             $operatorType = 0x00;
@@ -3141,6 +3115,11 @@ class Worksheet extends BIFFwriter
         // Text direction
         $flags |= (1 == 0 ? 0x80000000 : 0);
 
+        $dataBlockFont = null;
+        $dataBlockAlign = null;
+        $dataBlockBorder = null;
+        $dataBlockFill = null;
+
         // Data Blocks
         if ($bFormatFont == 1) {
             // Font Name
@@ -4398,15 +4377,6 @@ class Worksheet extends BIFFwriter
             $dataBlockFill = pack('v', $blockFillPatternStyle);
             $dataBlockFill .= pack('v', $colorIdxFg | ($colorIdxBg << 7));
         }
-        if ($bFormatProt == 1) {
-            $dataBlockProtection = 0;
-            if ($conditional->getStyle()->getProtection()->getLocked() == Protection::PROTECTION_PROTECTED) {
-                $dataBlockProtection = 1;
-            }
-            if ($conditional->getStyle()->getProtection()->getHidden() == Protection::PROTECTION_PROTECTED) {
-                $dataBlockProtection = 1 << 1;
-            }
-        }
 
         $data = pack('CCvvVv', $type, $operatorType, $szValue1, $szValue2, $flags, 0x0000);
         if ($bFormatFont == 1) { // Block Formatting : OK
@@ -4422,7 +4392,7 @@ class Worksheet extends BIFFwriter
             $data .= $dataBlockFill;
         }
         if ($bFormatProt == 1) {
-            $data .= $dataBlockProtection;
+            $data .= $this->getDataBlockProtection($conditional);
         }
         if ($operand1 !== null) {
             $data .= $operand1;
@@ -4486,4 +4456,17 @@ class Worksheet extends BIFFwriter
         $data .= $cellRange;
         $this->append($header . $data);
     }
+
+    private function getDataBlockProtection(Conditional $conditional): int
+    {
+        $dataBlockProtection = 0;
+        if ($conditional->getStyle()->getProtection()->getLocked() == Protection::PROTECTION_PROTECTED) {
+            $dataBlockProtection = 1;
+        }
+        if ($conditional->getStyle()->getProtection()->getHidden() == Protection::PROTECTION_PROTECTED) {
+            $dataBlockProtection = 1 << 1;
+        }
+
+        return $dataBlockProtection;
+    }
 }
diff --git a/src/PhpSpreadsheet/Writer/Xls/Xf.php b/src/PhpSpreadsheet/Writer/Xls/Xf.php
index 90d21bcf..eca3d8e0 100644
--- a/src/PhpSpreadsheet/Writer/Xls/Xf.php
+++ b/src/PhpSpreadsheet/Writer/Xls/Xf.php
@@ -115,6 +115,21 @@ class Xf
      */
     private $rightBorderColor;
 
+    /**
+     * @var int
+     */
+    private $diag;
+
+    /**
+     * @var int
+     */
+    private $diagColor;
+
+    /**
+     * @var Style
+     */
+    private $style;
+
     /**
      * Constructor.
      *
@@ -132,14 +147,14 @@ class Xf
         $this->foregroundColor = 0x40;
         $this->backgroundColor = 0x41;
 
-        $this->_diag = 0;
+        $this->diag = 0;
 
         $this->bottomBorderColor = 0x40;
         $this->topBorderColor = 0x40;
         $this->leftBorderColor = 0x40;
         $this->rightBorderColor = 0x40;
-        $this->_diag_color = 0x40;
-        $this->_style = $style;
+        $this->diagColor = 0x40;
+        $this->style = $style;
     }
 
     /**
@@ -153,39 +168,39 @@ class Xf
         if ($this->isStyleXf) {
             $style = 0xFFF5;
         } else {
-            $style = self::mapLocked($this->_style->getProtection()->getLocked());
-            $style |= self::mapHidden($this->_style->getProtection()->getHidden()) << 1;
+            $style = self::mapLocked($this->style->getProtection()->getLocked());
+            $style |= self::mapHidden($this->style->getProtection()->getHidden()) << 1;
         }
 
         // Flags to indicate if attributes have been set.
         $atr_num = ($this->numberFormatIndex != 0) ? 1 : 0;
         $atr_fnt = ($this->fontIndex != 0) ? 1 : 0;
-        $atr_alc = ((int) $this->_style->getAlignment()->getWrapText()) ? 1 : 0;
-        $atr_bdr = (self::mapBorderStyle($this->_style->getBorders()->getBottom()->getBorderStyle()) ||
-                        self::mapBorderStyle($this->_style->getBorders()->getTop()->getBorderStyle()) ||
-                        self::mapBorderStyle($this->_style->getBorders()->getLeft()->getBorderStyle()) ||
-                        self::mapBorderStyle($this->_style->getBorders()->getRight()->getBorderStyle())) ? 1 : 0;
+        $atr_alc = ((int) $this->style->getAlignment()->getWrapText()) ? 1 : 0;
+        $atr_bdr = (self::mapBorderStyle($this->style->getBorders()->getBottom()->getBorderStyle()) ||
+            self::mapBorderStyle($this->style->getBorders()->getTop()->getBorderStyle()) ||
+            self::mapBorderStyle($this->style->getBorders()->getLeft()->getBorderStyle()) ||
+            self::mapBorderStyle($this->style->getBorders()->getRight()->getBorderStyle())) ? 1 : 0;
         $atr_pat = ($this->foregroundColor != 0x40) ? 1 : 0;
         $atr_pat = ($this->backgroundColor != 0x41) ? 1 : $atr_pat;
-        $atr_pat = self::mapFillType($this->_style->getFill()->getFillType()) ? 1 : $atr_pat;
-        $atr_prot = self::mapLocked($this->_style->getProtection()->getLocked())
-                        | self::mapHidden($this->_style->getProtection()->getHidden());
+        $atr_pat = self::mapFillType($this->style->getFill()->getFillType()) ? 1 : $atr_pat;
+        $atr_prot = self::mapLocked($this->style->getProtection()->getLocked())
+            | self::mapHidden($this->style->getProtection()->getHidden());
 
         // Zero the default border colour if the border has not been set.
-        if (self::mapBorderStyle($this->_style->getBorders()->getBottom()->getBorderStyle()) == 0) {
+        if (self::mapBorderStyle($this->style->getBorders()->getBottom()->getBorderStyle()) == 0) {
             $this->bottomBorderColor = 0;
         }
-        if (self::mapBorderStyle($this->_style->getBorders()->getTop()->getBorderStyle()) == 0) {
+        if (self::mapBorderStyle($this->style->getBorders()->getTop()->getBorderStyle()) == 0) {
             $this->topBorderColor = 0;
         }
-        if (self::mapBorderStyle($this->_style->getBorders()->getRight()->getBorderStyle()) == 0) {
+        if (self::mapBorderStyle($this->style->getBorders()->getRight()->getBorderStyle()) == 0) {
             $this->rightBorderColor = 0;
         }
-        if (self::mapBorderStyle($this->_style->getBorders()->getLeft()->getBorderStyle()) == 0) {
+        if (self::mapBorderStyle($this->style->getBorders()->getLeft()->getBorderStyle()) == 0) {
             $this->leftBorderColor = 0;
         }
-        if (self::mapBorderStyle($this->_style->getBorders()->getDiagonal()->getBorderStyle()) == 0) {
-            $this->_diag_color = 0;
+        if (self::mapBorderStyle($this->style->getBorders()->getDiagonal()->getBorderStyle()) == 0) {
+            $this->diagColor = 0;
         }
 
         $record = 0x00E0; // Record identifier
@@ -194,9 +209,9 @@ class Xf
         $ifnt = $this->fontIndex; // Index to FONT record
         $ifmt = $this->numberFormatIndex; // Index to FORMAT record
 
-        $align = $this->mapHAlign($this->_style->getAlignment()->getHorizontal()); // Alignment
-        $align |= (int) $this->_style->getAlignment()->getWrapText() << 3;
-        $align |= self::mapVAlign($this->_style->getAlignment()->getVertical()) << 4;
+        $align = $this->mapHAlign($this->style->getAlignment()->getHorizontal()); // Alignment
+        $align |= (int) $this->style->getAlignment()->getWrapText() << 3;
+        $align |= self::mapVAlign($this->style->getAlignment()->getVertical()) << 4;
         $align |= $this->textJustLast << 7;
 
         $used_attrib = $atr_num << 2;
@@ -209,35 +224,35 @@ class Xf
         $icv = $this->foregroundColor; // fg and bg pattern colors
         $icv |= $this->backgroundColor << 7;
 
-        $border1 = self::mapBorderStyle($this->_style->getBorders()->getLeft()->getBorderStyle()); // Border line style and color
-        $border1 |= self::mapBorderStyle($this->_style->getBorders()->getRight()->getBorderStyle()) << 4;
-        $border1 |= self::mapBorderStyle($this->_style->getBorders()->getTop()->getBorderStyle()) << 8;
-        $border1 |= self::mapBorderStyle($this->_style->getBorders()->getBottom()->getBorderStyle()) << 12;
+        $border1 = self::mapBorderStyle($this->style->getBorders()->getLeft()->getBorderStyle()); // Border line style and color
+        $border1 |= self::mapBorderStyle($this->style->getBorders()->getRight()->getBorderStyle()) << 4;
+        $border1 |= self::mapBorderStyle($this->style->getBorders()->getTop()->getBorderStyle()) << 8;
+        $border1 |= self::mapBorderStyle($this->style->getBorders()->getBottom()->getBorderStyle()) << 12;
         $border1 |= $this->leftBorderColor << 16;
         $border1 |= $this->rightBorderColor << 23;
 
-        $diagonalDirection = $this->_style->getBorders()->getDiagonalDirection();
+        $diagonalDirection = $this->style->getBorders()->getDiagonalDirection();
         $diag_tl_to_rb = $diagonalDirection == Borders::DIAGONAL_BOTH
-                            || $diagonalDirection == Borders::DIAGONAL_DOWN;
+            || $diagonalDirection == Borders::DIAGONAL_DOWN;
         $diag_tr_to_lb = $diagonalDirection == Borders::DIAGONAL_BOTH
-                            || $diagonalDirection == Borders::DIAGONAL_UP;
+            || $diagonalDirection == Borders::DIAGONAL_UP;
         $border1 |= $diag_tl_to_rb << 30;
         $border1 |= $diag_tr_to_lb << 31;
 
         $border2 = $this->topBorderColor; // Border color
         $border2 |= $this->bottomBorderColor << 7;
-        $border2 |= $this->_diag_color << 14;
-        $border2 |= self::mapBorderStyle($this->_style->getBorders()->getDiagonal()->getBorderStyle()) << 21;
-        $border2 |= self::mapFillType($this->_style->getFill()->getFillType()) << 26;
+        $border2 |= $this->diagColor << 14;
+        $border2 |= self::mapBorderStyle($this->style->getBorders()->getDiagonal()->getBorderStyle()) << 21;
+        $border2 |= self::mapFillType($this->style->getFill()->getFillType()) << 26;
 
         $header = pack('vv', $record, $length);
 
         //BIFF8 options: identation, shrinkToFit and  text direction
-        $biff8_options = $this->_style->getAlignment()->getIndent();
-        $biff8_options |= (int) $this->_style->getAlignment()->getShrinkToFit() << 4;
+        $biff8_options = $this->style->getAlignment()->getIndent();
+        $biff8_options |= (int) $this->style->getAlignment()->getShrinkToFit() << 4;
 
         $data = pack('vvvC', $ifnt, $ifmt, $style, $align);
-        $data .= pack('CCC', self::mapTextRotation($this->_style->getAlignment()->getTextRotation()), $biff8_options, $used_attrib);
+        $data .= pack('CCC', self::mapTextRotation($this->style->getAlignment()->getTextRotation()), $biff8_options, $used_attrib);
         $data .= pack('VVv', $border1, $border2, $icv);
 
         return $header . $data;
@@ -300,7 +315,7 @@ class Xf
      */
     public function setDiagColor($colorIndex): void
     {
-        $this->_diag_color = $colorIndex;
+        $this->diagColor = $colorIndex;
     }
 
     /**
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Chart.php b/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
index 583b262c..19da32c4 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
@@ -219,10 +219,12 @@ class Chart extends WriterPart
         $chartTypes = self::getChartType($plotArea);
         $catIsMultiLevelSeries = $valIsMultiLevelSeries = false;
         $plotGroupingType = '';
+        $chartType = null;
         foreach ($chartTypes as $chartType) {
             $objWriter->startElement('c:' . $chartType);
 
             $groupCount = $plotArea->getPlotGroupCount();
+            $plotGroup = null;
             for ($i = 0; $i < $groupCount; ++$i) {
                 $plotGroup = $plotArea->getPlotGroupByIndex($i);
                 $groupType = $plotGroup->getPlotType();
@@ -244,7 +246,7 @@ class Chart extends WriterPart
 
             $this->writeDataLabels($objWriter, $layout);
 
-            if ($chartType === DataSeries::TYPE_LINECHART) {
+            if ($chartType === DataSeries::TYPE_LINECHART && $plotGroup) {
                 //    Line only, Line3D can't be smoothed
                 $objWriter->startElement('c:smooth');
                 $objWriter->writeAttribute('val', (int) $plotGroup->getSmoothLine());
@@ -1079,6 +1081,7 @@ class Chart extends WriterPart
             }
         }
 
+        $plotSeriesIdx = 0;
         foreach ($plotSeriesOrder as $plotSeriesIdx => $plotSeriesRef) {
             $objWriter->startElement('c:ser');
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekDayTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekDayTest.php
index f1bc51f3..2e52a5d7 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekDayTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekDayTest.php
@@ -2,7 +2,7 @@
 
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
-use PhpOffice\PhpSpreadsheet\Calculation\DateTimeExcel\Weekday;
+use PhpOffice\PhpSpreadsheet\Calculation\DateTimeExcel\WeekDay;
 
 class WeekDayTest extends AllSetupTeardown
 {
@@ -28,8 +28,8 @@ class WeekDayTest extends AllSetupTeardown
     public function testWEEKDAYwith1904Calendar(): void
     {
         self::setMac1904();
-        self::assertEquals(7, Weekday::funcWeekDay('1904-01-02'));
-        self::assertEquals(6, Weekday::funcWeekDay('1904-01-01'));
-        self::assertEquals(6, Weekday::funcWeekDay(null));
+        self::assertEquals(7, WeekDay::funcWeekDay('1904-01-02'));
+        self::assertEquals(6, WeekDay::funcWeekDay('1904-01-01'));
+        self::assertEquals(6, WeekDay::funcWeekDay(null));
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Reader/Security/XmlScannerTest.php b/tests/PhpSpreadsheetTests/Reader/Security/XmlScannerTest.php
index f98ff7e1..c32c5743 100644
--- a/tests/PhpSpreadsheetTests/Reader/Security/XmlScannerTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Security/XmlScannerTest.php
@@ -37,7 +37,7 @@ class XmlScannerTest extends TestCase
         self::assertEquals($expectedResult, $result);
 
         // php 8.+ deprecated libxml_disable_entity_loader() - It's on by default
-        if (\PHP_VERSION_ID < 80000) {
+        if (isset($oldDisableEntityLoaderState)) {
             libxml_disable_entity_loader($oldDisableEntityLoaderState);
         }
     }