Description:
------------
In PHP4 one could call array_merge with non-array or unset variables and it would still correctly merge any arrays that were passed (i.e., type-checking was done within the function). I tested this in 4.3.8 for BSD.

In PHP5 if any of the parameters are not arrays, the function returns null.  I tested with 5.0.2 Mac OS X entropy release 1. 
   http://www.entropy.ch/software/macosx/php/

It was very handy to be able to pass a bunch of variables and get back the merged result of all the arrays without having to check each one to make sure it was set.

As is, instead of one line:

   $ar_merged = array_merge( $ar1, $ar2, $ar3, $ar4 );

one would have to have a long if-block:

$ar_merged = array();
if( is_array( $ar1 ) )
    $ar_merged = array_merge( $ar_merged, $ar1 );
if( is_array( $ar_2 ) )
    ...


Reproduce code:
---------------
<?php
$ar1 = array( "one", "two" );
$ar2 = "three";   // Optionally: comment out this line.

$ar_merged = array_merge( $ar1, $ar2 );
	
if( isset( $ar_merged ) )
    print_r( $ar_merged );
else
    print "Blarmy! Unset array!";
?>

Expected result:
----------------
In 4.3.8 it returned:

Array
(
    [0] => one
    [1] => two
    [2] => three
)

but I think it should still at least use the variables that are arrays:

Array
(
    [0] => one
    [1] => two
)

Also, if $ar2 is not defined at all it should return:

Array
(
    [0] => one
    [1] => two
)


Actual result:
--------------
Blarmy! Unset array!

It's ignoring ALL passed variables if ANY of them are not arrays, and returning a null result.