I would advice against using and in this context, because later someone (you) may add an innocent return ....

sub is_empty_string {
  my ($value) = @_;
  return defined $value and $value eq '';
}
[download]

I think && is more appropriate here:

sub is_empty_string {
  my ($value) = @_;
  return defined($value) && $value eq '';
}
[download]