$ perl -MData::Dumper -e'print Dumper sub{return 1 if $_[0]}->(undef)'
$VAR1 = undef;

$ perl -MData::Dumper -e'print Dumper sub{return 1 if $_[0]}->(0    )'
$VAR1 = 0;

$ perl -MData::Dumper -e'print Dumper sub{return 1 if $_[0]}->("0"  )'
$VAR1 = '0';

$ perl -MData::Dumper -e'print Dumper sub{return 1 if $_[0]}->(""   )'
$VAR1 = '';