Description:
------------
array_fill_keys must always return an array as described in 
http://de3.php.net/manual/en/function.array-fill-keys.php.

When call array_fill_keys with invalid arguments the function returns an invalid 
null!

Test script:
---------------
<?php

var_dump(array_fill_keys(array('a', 'b', 'c')));
var_dump(array_fill_keys(true, 1));
var_dump(array_fill_keys('', 2));
var_dump(array_fill_keys(NULL, 3));
var_dump(array_fill_keys());



Expected result:
----------------
Warning: array_fill_keys() expects parameter 1 to be array, boolean given in - on 
line 4
array(0) {
}

Warning: array_fill_keys() expects parameter 1 to be array, string given in - on 
line 5
array(0) {
}

Warning: array_fill_keys() expects parameter 1 to be array, null given in - on 
line 6
array(0) {
}

Warning: array_fill_keys() expects exactly 2 parameters, 0 given in - on line 7
array(0) {
}


Actual result:
--------------
Warning: array_fill_keys() expects exactly 2 parameters, 1 given in - on line 3
NULL

Warning: array_fill_keys() expects parameter 1 to be array, boolean given in - on 
line 4
NULL

Warning: array_fill_keys() expects parameter 1 to be array, string given in - on 
line 5
NULL

Warning: array_fill_keys() expects parameter 1 to be array, null given in - on 
line 6
NULL

Warning: array_fill_keys() expects exactly 2 parameters, 0 given in - on line 7
NULL