Avoid a PHP8.4 Deprecation

src/PhpSpreadsheet/Calculation/Calculation.php

@@ -5072,7 +5072,7 @@ private function processTokenStack(mixed $tokens, $cellID = null, ?Cell $cell =
                     krsort($args);
                     krsort($emptyArguments);
 
-                    if ($argCount > 0) {
+                    if ($argCount > 0 && is_array($functionCall)) {
                         $args = $this->addDefaultArgumentValues($functionCall, $args, $emptyArguments);
                     }
 
@@ -5571,7 +5571,7 @@ public function getImplementedFunctionNames(): array
 
     private function addDefaultArgumentValues(array $functionCall, array $args, array $emptyArguments): array
     {
-        $reflector = new ReflectionMethod(implode('::', $functionCall));
+        $reflector = new ReflectionMethod($functionCall[0], $functionCall[1]);
         $methodArguments = $reflector->getParameters();
 
         if (count($methodArguments) > 0) {

tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/PiTest.php

@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
+
+class PiTest extends AllSetupTeardown
+{
+    /**
+     * @dataProvider providerPI
+     */
+    public function testPI(mixed $expectedResult, mixed $number = 'omitted'): void
+    {
+        $this->mightHaveException($expectedResult);
+        $sheet = $this->getSheet();
+        if ($number !== null) {
+            $sheet->getCell('A1')->setValue($number);
+        }
+        if ($number === 'omitted') {
+            $sheet->getCell('B1')->setValue('=PI()');
+        } else {
+            $sheet->getCell('B1')->setValue('=PI(A1)');
+        }
+        $result = $sheet->getCell('B1')->getCalculatedValue();
+        self::assertEqualsWithDelta($expectedResult, $result, 1E-12);
+    }
+
+    public static function providerPI(): array
+    {
+        return require 'tests/data/Calculation/MathTrig/PI.php';
+    }
+}

tests/data/Calculation/MathTrig/PI.php

@@ -0,0 +1,8 @@
+<?php
+
+declare(strict_types=1);
+
+return [
+    [3.141592653589793],
+    'should not supply any arguments' => ['exception', 1],
+];