Description:
------------
if i use array_merge with two arrays, where one array-variable isn't set, the function returns NULL instead of the values of the other array.

Reproduce code:
---------------
<?php 
error_reporting(E_ALL & E_NOTICE); 
$array2 = array(1, 'a', TRUE); 
$array3 = array_merge($array2, $array1); // $array1 isn't set
var_dump($array3); 
?>  


Expected result:
----------------
works like this in PHP4:



undefined variable array1; 

should return array(1, 'a', true);

Actual result:
--------------
behaves like this in PHP5 snap:



undefined variable array1; 

returns NULL;