if (exists $xlist{$name} && defined $xlist{$name}) {
 $xlist{$name} = undef; # this exists now

##</code><code>##

if (defined $xlist{$name}) {

##</code><code>##

22:44 >perl -Mstrict -MData::Dump -wE "my %h = (a => 1, b => undef); dd \%h; say $_, defined $h{$_} ? ': yes' : ': no' for qw(a b c); dd \%h;"
{ a => 1, b => undef }
a: yes
b: no
c: no
{ a => 1, b => undef }

22:47 >