This is precisely where tlm's suggestion(++) comes in handy:
You could do: 
my $array = $hash->{$key} ||=[];

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This would initialize the hash value to an empty array ref, when necessary.

     "Income tax returns are the most imaginative fiction being written today." -- Herman Wouk

In reply to Re^4: creating defined references to arrays of size zero by NetWallah
in thread creating defined references to arrays of size zero by spieper

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