That will turn an attempt to autovivify into an exception. 
$ perl -MHash::Util=lock_keys -wle 'my %x; lock_keys %x; exists $x{a}{
+b}'
Attempt to access disallowed key 'a' in a restricted hash at -e line 1
+.

[download]

Very useful for debugging.

In reply to Re^2: exists on hash autovivifies right? by moritz
in thread exists on hash autovivifies right? by Anonymous Monk

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