What happens when you give NULL to a PHP function that expects string?
<p>For example to: <code>preg_match</code> or when you use concatenation?</p>

<p>Answer to comments:</p>

<p>I can test for <code>preg_match</code> or concatenation results, yes.</p>

<p>But there is a difference between:</p>

<p>PHP function with the signature: <code>int f(string $parameter)</code></p>

<ul>
<li>Will PHP convert the NULL to empty string <strong>before</strong> the <code>f</code> function gets it, or</li>
<li>Will the <code>f</code> function get NULL even if signature expects string, so the function may throw exceptions or behave not as it would received an empty string.</li>
</ul>

<p>(I can't test this, because I can't write <code>string</code> type for a parameter at function signature.)</p>
