What is the output of the following script?
<code>
1 <?php
2 class a
3 {
4 public $val;
5 }
6
7 function renderVal (a $a)
8 {
9 if ($a) {
10 echo $a->val;
11 }
12 }
13
14 renderVal (null);
15 ?>
</code>

A.
A syntax error in the function declaration line

B.
An error, because null is not an instance of ‘a’

C.
Nothing, because a null value is being passed torenderVal()

D.
NULL