Add a null value to ensure that ExcludeIf properly rejects it as an invalid condition (#54973)

Author: alikhosravidev

tests/Validation/ValidationExcludeIfTest.php

@@ -42,7 +42,7 @@ public function testItValidatesCallableAndBooleanAreAcceptableArguments()
         new ExcludeIf(true);
         new ExcludeIf(fn () => true);
 
-        foreach ([1, 1.1, 'phpinfo', new stdClass] as $condition) {
+        foreach ([1, 1.1, 'phpinfo', new stdClass, null] as $condition) {
             try {
                 new ExcludeIf($condition);
                 $this->fail('The ExcludeIf constructor must not accept '.gettype($condition));