Handle the case of an invalid formula by defaulting to ptgInt + 0, which will avoid breaking the file

samples/ConditionalFormatting/07_Expression_Comparisons.php

@@ -102,9 +102,9 @@ $expressionWizard->expression('ISEVEN(A1)')
     ->setStyle($yellowStyle);
 $conditionalStyles[] = $expressionWizard->getConditional();
 
-//$spreadsheet->getActiveSheet()
-//    ->getStyle($expressionWizard->getCellRange())
-//    ->setConditionalStyles($conditionalStyles);
+$spreadsheet->getActiveSheet()
+    ->getStyle($expressionWizard->getCellRange())
+    ->setConditionalStyles($conditionalStyles);
 
 // Set rules for Sales Grid Row match against Country Comparison
 $cellRange = 'A17:D22';

src/PhpSpreadsheet/Writer/Xls/ConditionalHelper.php

@@ -55,11 +55,11 @@ class ConditionalHelper
                 $formula = Wizard\WizardAbstract::reverseAdjustCellRef((string) $condition, $cellRange);
                 $this->parser->parse($formula);
                 $this->tokens = $this->parser->toReversePolish();
-                $this->size = strlen($this->tokens);
+                $this->size = strlen($this->tokens ?? '');
             } catch (PhpSpreadsheetException $e) {
-                var_dump("PARSER EXCEPTION: {$e->getMessage()}");
-                $this->tokens = null;
-                $this->size = 0;
+                // In the event of a parser error with a formula value, we set the expression to ptgInt + 0
+                $this->tokens = pack('Cv', 0x1E, 0);
+                $this->size = 3;
             }
         }
     }

src/PhpSpreadsheet/Writer/Xls/Worksheet.php

@@ -2787,8 +2787,8 @@ class Worksheet extends BIFFwriter
         string $cellRange
     ): void {
         $record = 0x01B1; // Record identifier
-        $type = null;  //  Type of the CF
-        $operatorType = null;   //  Comparison operator
+        $type = null; // Type of the CF
+        $operatorType = null; // Comparison operator
 
         if ($conditional->getConditionType() == Conditional::CONDITION_EXPRESSION) {
             $type = 0x02;