You are not using NULL keys (whatever those are) in your example but empty strings. Also, it's very easy to put empty strings in arrays:

my @array = ('a','','b','');
print "'$_'\n" for @array;
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Other then that - I don't understand what your question is. Please show us some code that doesn't work, maybe we can help you with that. :-)

-- 
Joost       downtime n. The period during which a system
            is error-free and immune from user input.
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