Description:
------------
mysqli_bind_result doesn't support MYSQL_TYPE_NULL. This causes libmysql to fail with error buffer_length=0.

Reproduce code:
---------------
<?php

$mysql = new mysqli("localhost", "root", "");

$stmt = $mysql->prepare("SELECT NULL FROM DUAL");
$stmt->execute();

$stmt->bind_result($val);
$stmt->fetch();

var_dump($val);

$stmt->close();
$mysql->close();
?>