$ perl -wE 'my $x={};my %h; say "plain $h{new} deref $x->{new}"'
Use of uninitialized value $h{"new"} in concatenation (.) or string at -e line 1.
Use of uninitialized value in concatenation (.) or string at -e line 1.
plain  deref 

##</code><code>##

$ perlbrew use perl-5.8.9
$ perl -we 'my $x={};my %h; print "plain $h{new} deref $x->{new}"'
Use of uninitialized value in concatenation (.) or string at -e line 1.
Use of uninitialized value in concatenation (.) or string at -e line 1.