Filter null values in PRODUCT() function, as they don't affect the calculation in any way, and actually require additional code handling if they're present within the calculation itself

src/PhpSpreadsheet/Calculation/MathTrig/Operations.php

@@ -102,29 +102,27 @@ class Operations
      */
     public static function product(...$args)
     {
+        $args = array_filter(
+            Functions::flattenArray($args),
+            function ($value) {
+                return $value !== null;
+            }
+        );
+
         // Return value
-        $returnValue = null;
+        $returnValue = (count($args) === 0) ? 0.0 : 1.0;
 
         // Loop through arguments
-        foreach (Functions::flattenArray($args) as $arg) {
+        foreach ($args as $arg) {
             // Is it a numeric value?
-            if (is_numeric($arg) || $arg === null) {
-                if ($returnValue === null) {
-                    $returnValue = $arg;
-                } else {
+            if (is_numeric($arg)) {
                 $returnValue *= $arg;
-                }
             } else {
                 return ExcelError::VALUE();
             }
         }
 
-        // Return
-        if ($returnValue === null) {
-            return 0;
-        }
-
-        return $returnValue;
+        return (float) $returnValue;
     }
 
     /**

tests/data/Calculation/MathTrig/PRODUCT.php

@@ -49,17 +49,29 @@ return [
         -2,
     ],
     [
-        0,
+        31.25,
         12.5,
         null,
         2.5,
     ],
     [
-        0,
+        31.25,
         12.5,
         2.5,
         null,
     ],
+    [
+        12.5,
+        12.5,
+        null,
+        null,
+    ],
+    [
+        0.0,
+        null,
+        null,
+        null,
+    ],
     ['#VALUE!', 1, 'y', 3],
     [6, 1, '2', 3],
 ];