Fix CI

phpstan-baseline.neon

@@ -5757,7 +5757,7 @@ parameters:
 
 		-
 			message: "#^Parameter \\#2 \\$value of method XMLWriter\\:\\:writeAttribute\\(\\) expects string, string\\|null given\\.$#"
-			count: 4
+			count: 5
 			path: src/PhpSpreadsheet/Writer/Xlsx/StringTable.php
 
 		-
@@ -5852,9 +5852,14 @@ parameters:
 
 		-
 			message: "#^Parameter \\#2 \\$value of method XMLWriter\\:\\:writeAttribute\\(\\) expects string, string\\|null given\\.$#"
-			count: 4
+			count: 9
 			path: src/PhpSpreadsheet/Writer/Xlsx/Style.php
 
+		-
+			message: "#^Parameter \\#2 \\$value of method XMLWriter\\:\\:writeAttribute\\(\\) expects string, string\\|null given\\.$#"
+			count: 1
+			path: src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
+
 		-
 			message: "#^Parameter \\#2 \\$value of method XMLWriter\\:\\:writeAttribute\\(\\) expects string, float given\\.$#"
 			count: 1

src/PhpSpreadsheet/Style/Color.php

@@ -41,7 +41,7 @@ class Color extends Supervisor
     /**
      * ARGB - Alpha RGB.
      *
-     * @var string
+     * @var null|string
      */
     protected $argb;
 
@@ -135,7 +135,7 @@ class Color extends Supervisor
     /**
      * Get ARGB.
      */
-    public function getARGB(): string
+    public function getARGB(): ?string
     {
         if ($this->isSupervisor) {
             return $this->getSharedComponent()->getARGB();

src/PhpSpreadsheet/Writer/Html.php

@@ -1296,7 +1296,7 @@ class Html extends BaseWriter
         } else {
             $origData = $this->preCalculateFormulas ? $cell->getCalculatedValue() : $cell->getValue();
             $formatCode = $worksheet->getParent()->getCellXfByIndex($cell->getXfIndex())->getNumberFormat()->getFormatCode();
-            if ($formatCode) {
+            if ($formatCode !== null) {
                 $cellData = NumberFormat::toFormattedString(
                     $origData,
                     $formatCode,