--TEST-- Returned null, expected array reference --FILE-- <?php function &foo(array &$in) : array { return null; } $array = [1, 2, 3]; var_dump(foo($array)); --EXPECTF-- Fatal error: Uncaught TypeError: Return value of foo() must be of the type array, null returned in %s:%d Stack trace: #0 %s(%d): foo(Array) #1 {main} thrown in %s on line %d