diff --git a/src/PhpSpreadsheet/Calculation/ArrayEnabled.php b/src/PhpSpreadsheet/Calculation/ArrayEnabled.php
index ad61eb7d..0ad429ed 100644
--- a/src/PhpSpreadsheet/Calculation/ArrayEnabled.php
+++ b/src/PhpSpreadsheet/Calculation/ArrayEnabled.php
@@ -12,12 +12,15 @@ trait ArrayEnabled
      */
     private static $arrayArgumentHelper;
 
-    private static function initialiseHelper(array $arguments): void
+    /**
+     * @param array|false $arguments Can be changed to array for Php8.1+
+     */
+    private static function initialiseHelper($arguments): void
     {
         if (self::$arrayArgumentHelper === null) {
             self::$arrayArgumentHelper = new ArrayArgumentHelper();
         }
-        self::$arrayArgumentHelper->initialise($arguments);
+        self::$arrayArgumentHelper->initialise($arguments ?: []);
     }
 
     /**
@@ -70,6 +73,14 @@ trait ArrayEnabled
         return ArrayArgumentProcessor::processArguments(self::$arrayArgumentHelper, $method, ...$arguments);
     }
 
+    /**
+     * @param mixed $value
+     */
+    private static function testFalse($value): bool
+    {
+        return $value === false;
+    }
+
     /**
      * Handles array argument processing when the function accepts multiple arguments,
      *     but only the last few (from start) can be an array arguments.
@@ -85,7 +96,7 @@ trait ArrayEnabled
             range($start, count($arguments) - $start),
             array_slice($arguments, $start)
         );
-        if ($arrayArgumentsSubset === false) {
+        if (self::testFalse($arrayArgumentsSubset)) {
             return ['#VALUE!'];
         }
 
diff --git a/src/PhpSpreadsheet/Calculation/Information/Value.php b/src/PhpSpreadsheet/Calculation/Information/Value.php
index e29144b8..0ac6b669 100644
--- a/src/PhpSpreadsheet/Calculation/Information/Value.php
+++ b/src/PhpSpreadsheet/Calculation/Information/Value.php
@@ -87,7 +87,7 @@ class Value
             return ExcelError::VALUE();
         }
 
-        return $value % 2 == 0;
+        return ((int) fmod($value, 2)) === 0;
     }
 
     /**
@@ -112,7 +112,7 @@ class Value
             return ExcelError::VALUE();
         }
 
-        return abs($value) % 2 == 1;
+        return ((int) fmod($value, 2)) !== 0;
     }
 
     /**
diff --git a/src/PhpSpreadsheet/Cell/Coordinate.php b/src/PhpSpreadsheet/Cell/Coordinate.php
index b4b76c57..6c3fce60 100644
--- a/src/PhpSpreadsheet/Cell/Coordinate.php
+++ b/src/PhpSpreadsheet/Cell/Coordinate.php
@@ -92,6 +92,7 @@ abstract class Coordinate
         }
 
         // Create absolute coordinate
+        $cellAddress = "$cellAddress";
         if (ctype_digit($cellAddress)) {
             return $worksheet . '$' . $cellAddress;
         } elseif (ctype_alpha($cellAddress)) {
diff --git a/src/PhpSpreadsheet/Helper/Dimension.php b/src/PhpSpreadsheet/Helper/Dimension.php
index 136ffd7f..4e3e6680 100644
--- a/src/PhpSpreadsheet/Helper/Dimension.php
+++ b/src/PhpSpreadsheet/Helper/Dimension.php
@@ -58,7 +58,7 @@ class Dimension
     public function __construct(string $dimension)
     {
         [$size, $unit] = sscanf($dimension, '%[1234567890.]%s');
-        $unit = strtolower(trim($unit));
+        $unit = strtolower(trim($unit ?? ''));
 
         // If a UoM is specified, then convert the size to pixels for internal storage
         if (isset(self::ABSOLUTE_UNITS[$unit])) {
diff --git a/src/PhpSpreadsheet/Helper/Html.php b/src/PhpSpreadsheet/Helper/Html.php
index 73a3308c..4eecf99d 100644
--- a/src/PhpSpreadsheet/Helper/Html.php
+++ b/src/PhpSpreadsheet/Helper/Html.php
@@ -794,7 +794,7 @@ class Html
         $domText = preg_replace(
             '/\s+/u',
             ' ',
-            str_replace(["\r", "\n"], ' ', $textNode->nodeValue)
+            str_replace(["\r", "\n"], ' ', $textNode->nodeValue ?: '')
         );
         $this->stringData .= $domText;
         $this->buildTextRun();
diff --git a/src/PhpSpreadsheet/Reader/Html.php b/src/PhpSpreadsheet/Reader/Html.php
index 9d02fee9..15c9f625 100644
--- a/src/PhpSpreadsheet/Reader/Html.php
+++ b/src/PhpSpreadsheet/Reader/Html.php
@@ -619,7 +619,7 @@ class Html extends BaseReader
     {
         foreach ($element->childNodes as $child) {
             if ($child instanceof DOMText) {
-                $domText = preg_replace('/\s+/u', ' ', trim($child->nodeValue));
+                $domText = preg_replace('/\s+/u', ' ', trim($child->nodeValue ?: ''));
                 if (is_string($cellContent)) {
                     //    simply append the text if the cell content is a plain text string
                     $cellContent .= $domText;
diff --git a/src/PhpSpreadsheet/Reader/Ods.php b/src/PhpSpreadsheet/Reader/Ods.php
index d0d87c5f..791c0780 100644
--- a/src/PhpSpreadsheet/Reader/Ods.php
+++ b/src/PhpSpreadsheet/Reader/Ods.php
@@ -617,7 +617,7 @@ class Ods extends BaseReader
         foreach ($settings->getElementsByTagNameNS($configNs, 'config-item') as $t) {
             if ($t->getAttributeNs($configNs, 'name') === 'ActiveTable') {
                 try {
-                    $spreadsheet->setActiveSheetIndexByName($t->nodeValue);
+                    $spreadsheet->setActiveSheetIndexByName($t->nodeValue ?: '');
                 } catch (Throwable $e) {
                     // do nothing
                 }
diff --git a/src/PhpSpreadsheet/Worksheet/AutoFilter.php b/src/PhpSpreadsheet/Worksheet/AutoFilter.php
index 1bc71184..2e6c8289 100644
--- a/src/PhpSpreadsheet/Worksheet/AutoFilter.php
+++ b/src/PhpSpreadsheet/Worksheet/AutoFilter.php
@@ -386,7 +386,7 @@ class AutoFilter
             /** @var string */
             $ruleOperator = $rule['operator'];
             /** @var string */
-            $cellValueString = $cellValue;
+            $cellValueString = $cellValue ?? '';
             $retVal = false;
 
             if (is_numeric($ruleValue)) {
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
index c5502a33..06c8becf 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
@@ -1279,7 +1279,7 @@ class Worksheet extends WriterPart
                 $objWriter,
                 $this->getParentWriter()->getOffice2003Compatibility() === false,
                 'v',
-                ($this->getParentWriter()->getPreCalculateFormulas() && !is_array($calculatedValue) && substr($calculatedValue, 0, 1) !== '#')
+                ($this->getParentWriter()->getPreCalculateFormulas() && !is_array($calculatedValue) && substr($calculatedValue ?? '', 0, 1) !== '#')
                     ? StringHelper::formatNumber($calculatedValue) : '0'
             );
         }