Description:
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This creates a need to define variables before being used  
which is opposite of PHP's original behavior and spirit.   
This strange array_merge behavior is one step closer to  
making PHP a strongly typed language if the function  
behaves differently depending on whether or not aruments  
are defined and empty or not defined at all.  

Reproduce code:
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$array2 = array('a');

$empty_var = array_merge($array1,$array2);



Expected result:
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$empty_var should be an array with the same contents as 
array2. 

Actual result:
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$empty_var contains no data at all.  This is different 
from PHP4 behavior with no benefits.