When accessing deep-nested data structures, take no chances with autovivification. Make use of Data::Diver

For example, fire up your Perl debugger:

  $ perl -de ''
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Then enter these lines:

  undef $ref
  exists $ref->{intervened}->{notvivified} # should not exist
  x $ref
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You'll see that $ref->{intervened} has been autovivified. Scary, isn't it? This also applies to dereferencing arrays.