I think this is a fairly standard approach

{
  ## accepted attributes
  my %options = map { $_ => undef } qw/ from_node to_node label /;
  sub new {
    my $class = shift;
    bless {
      %options,
      map { exists $options{$_} ? ( $_ => 1 ) : () } @_
    }, $class
  }
}
[download]

And hopefully that should do the right thing for your given case.
HTH

_________
broquaint

update: code complies with OP request