While a variable is a string and if it has neither been assigned a value nor numified its value will be '', I am not sure on this but I think '' or undef or 0 can be interchanging depending on the context that the null variable scalar is used under (i.e when a scalar which's null is numified its value becomes 0).

Isn't this behaviour mainly hiding ugly bugs?

This behavior seems consistent and indeed in/of use, for instance, consider when quickly wanting to start a counter:

C:\Documents and Settings>perl -
print "$hash{count} \n";           
print -$hash{count},"\n";
print --$hash{count},"\n";
print ++$hash{count},"\n";
__END__

0
-1
0
C:\Documents and Settings>
[download]

Update: did s/' '/''/, thanks Jenda for noticing the unintended typo as '' and ' ' are not the same thing. Added technical corrections too..

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