2;0 juerd@ouranos:~$ cat test.pl
#!/usr/bin/perl -w
use GDBM_File;
use strict;
unlink 'karmatest';

my $hashref = { hash => {} };
$hashref->{object} = tie %{ $hashref->{hash} }, 'GDBM_File', 'karmatest', GDBM_WRCREAT, 0640;

sub resolve {
    return \ $hashref->{hash}{$_[0]};
}

# Warning!
${ resolve('this one does not exist') }  +=  2;

# now, the same, but without tie:

my $second = { hash => {} };

sub resolve_again {
    return \ $second->{hash}{$_[0]};
}

# No warning!
${ resolve('this one does not exist') }  +=  2;
2;0 juerd@ouranos:~$ perl test.pl
Use of uninitialized value in addition (+) at test.pl line 13.

##</code><code>##

2;0 juerd@ouranos:~$ perl -e'undef christmas'
Segmentation fault
2;139 juerd@ouranos:~$