diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5abcae5423..d489478735 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com)
 and this project adheres to [Semantic Versioning](https://semver.org). This is always true of the master branch. Some earlier branches, including the branch from which you are reading this file, remain supported and security fixes are applied to them; if the security fix represents a breaking change, it may have to be applied as a minor or patch version.
 
+## TBD - 2.4.2
+
+### Fixed
+
+ - Php8.5 deprecates use of null as array index. [PR #4635](https://github.com/PHPOffice/PhpSpreadsheet/pull/4635)
+
 ## 2025-09-03 - 2.4.1
 
 ### Added
diff --git a/src/PhpSpreadsheet/Calculation/Calculation.php b/src/PhpSpreadsheet/Calculation/Calculation.php
index daa7174fd7..80c9e140df 100644
--- a/src/PhpSpreadsheet/Calculation/Calculation.php
+++ b/src/PhpSpreadsheet/Calculation/Calculation.php
@@ -4635,7 +4635,7 @@ private function processTokenStack(mixed $tokens, ?string $cellID = null, ?Cell
                         return $this->raiseFormulaError($e->getMessage(), $e->getCode(), $e);
                     }
                 }
-            } elseif (!is_numeric($token) && !is_object($token) && isset(self::BINARY_OPERATORS[$token])) {
+            } elseif (!is_numeric($token) && !is_object($token) && isset($token, self::BINARY_OPERATORS[$token])) {
                 // if the token is a binary operator, pop the top two values off the stack, do the operation, and push the result back on the stack
                 //    We must have two operands, error if we don't
                 $operand2Data = $stack->pop();
diff --git a/src/PhpSpreadsheet/Calculation/Database/DatabaseAbstract.php b/src/PhpSpreadsheet/Calculation/Database/DatabaseAbstract.php
index 7d9885ee90..66af793a16 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DatabaseAbstract.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DatabaseAbstract.php
@@ -86,9 +86,9 @@ protected static function getFilteredColumn(array $database, ?int $field, array
         $columnData = [];
         foreach ($database as $rowKey => $row) {
             $keys = array_keys($row);
-            $key = $keys[$field] ?? null;
+            $key = ($field === null) ? null : ($keys[$field] ?? null);
             $columnKey = $key ?? 'A';
-            $columnData[$rowKey][$columnKey] = $row[$key] ?? $defaultReturnColumnValue;
+            $columnData[$rowKey][$columnKey] = ($key === null) ? $defaultReturnColumnValue : ($row[$key] ?? $defaultReturnColumnValue);
         }
 
         return $columnData;
diff --git a/src/PhpSpreadsheet/Calculation/Engine/BranchPruner.php b/src/PhpSpreadsheet/Calculation/Engine/BranchPruner.php
index e6dbbcbdee..97e4c95149 100644
--- a/src/PhpSpreadsheet/Calculation/Engine/BranchPruner.php
+++ b/src/PhpSpreadsheet/Calculation/Engine/BranchPruner.php
@@ -78,7 +78,7 @@ public function initialiseForLoop(): void
 
     private function initialiseCondition(): void
     {
-        if (isset($this->conditionMap[$this->pendingStoreKey]) && $this->conditionMap[$this->pendingStoreKey]) {
+        if (isset($this->pendingStoreKey, $this->conditionMap[$this->pendingStoreKey]) && $this->conditionMap[$this->pendingStoreKey]) {
             $this->currentCondition = $this->pendingStoreKey;
             $stackDepth = count($this->storeKeysStack);
             if ($stackDepth > 1) {
@@ -90,7 +90,7 @@ private function initialiseCondition(): void
 
     private function initialiseThen(): void
     {
-        if (isset($this->thenMap[$this->pendingStoreKey]) && $this->thenMap[$this->pendingStoreKey]) {
+        if (isset($this->pendingStoreKey, $this->thenMap[$this->pendingStoreKey]) && $this->thenMap[$this->pendingStoreKey]) {
             $this->currentOnlyIf = $this->pendingStoreKey;
         } elseif (
             isset($this->previousStoreKey, $this->thenMap[$this->previousStoreKey])
@@ -102,7 +102,7 @@ private function initialiseThen(): void
 
     private function initialiseElse(): void
     {
-        if (isset($this->elseMap[$this->pendingStoreKey]) && $this->elseMap[$this->pendingStoreKey]) {
+        if (isset($this->pendingStoreKey, $this->elseMap[$this->pendingStoreKey]) && $this->elseMap[$this->pendingStoreKey]) {
             $this->currentOnlyIfNot = $this->pendingStoreKey;
         } elseif (
             isset($this->previousStoreKey, $this->elseMap[$this->previousStoreKey])
diff --git a/src/PhpSpreadsheet/Reader/Xlsx.php b/src/PhpSpreadsheet/Reader/Xlsx.php
index c43cf06e98..b3dd58f3b6 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx.php
@@ -1227,7 +1227,7 @@ protected function loadSpreadsheetFromFile(string $filename): Spreadsheet
                                                 // Set comment properties
                                                 $comment = $docSheet->getComment([$column + 1, $row + 1]);
                                                 $comment->getFillColor()->setRGB($fillColor);
-                                                if (isset($drowingImages[$fillImageRelId])) {
+                                                if (isset($fillImageRelId, $drowingImages[$fillImageRelId])) {
                                                     $objDrawing = new \PhpOffice\PhpSpreadsheet\Worksheet\Drawing();
                                                     $objDrawing->setName($fillImageTitle);
                                                     $imagePath = str_replace(['../', '/xl/'], 'xl/', $drowingImages[$fillImageRelId]);
diff --git a/src/PhpSpreadsheet/Writer/Pdf/Dompdf.php b/src/PhpSpreadsheet/Writer/Pdf/Dompdf.php
index 194bb84419..57932a0bbc 100644
--- a/src/PhpSpreadsheet/Writer/Pdf/Dompdf.php
+++ b/src/PhpSpreadsheet/Writer/Pdf/Dompdf.php
@@ -76,7 +76,7 @@ public function save($filename, int $flags = 0): void
     public function specialErrorHandler(int $errno, string $errstr, string $filename, int $lineno): bool
     {
         if ($errno === E_DEPRECATED) {
-            if (preg_match('/canonical|imagedestroy|http_get_last_response_headers/', $errstr) === 1) {
+            if (preg_match('/canonical|imagedestroy|http_get_last_response_headers|Using null as an array offset/', $errstr) === 1) {
                 return true;
             }
         }
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Rels.php b/src/PhpSpreadsheet/Writer/Xlsx/Rels.php
index 1e6e3b493e..04fd105edb 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Rels.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Rels.php
@@ -206,7 +206,7 @@ public function writeWorksheetRelationships(\PhpOffice\PhpSpreadsheet\Worksheet\
             // (! synchronize with \PhpOffice\PhpSpreadsheet\Writer\Xlsx\Worksheet::writeDrawings)
             reset($drawingOriginalIds);
             $relPath = key($drawingOriginalIds);
-            if (isset($drawingOriginalIds[$relPath])) {
+            if (isset($relPath, $drawingOriginalIds[$relPath])) {
                 $rId = (int) (substr($drawingOriginalIds[$relPath], 3));
             }