Given the following code, what is correct?
function f(stdClass &$x = NULL) { $x = 42;}
$z = new stdClass;
f($z);
var _dump($z);
A . Error: Typehints cannot be NULL
B . Error: Typehints cannot be references
C . Result is NU LL
D . Result is object of type stdClass
E . Result is 42
Answer: E