sub _close {
  my $data = shift;
  my $ftp  = ${*$data}{'net_ftp_cmd'};

  $data->SUPER::close();

  delete ${*$ftp}{'net_ftp_dataconn'} ################# LINE 54
    if exists ${*$ftp}{'net_ftp_dataconn'}
    && $data == ${*$ftp}{'net_ftp_dataconn'};


##</code><code>##

$ perl -MNet::FTP -MNet::FTP::dataconn -le ' Net::FTP::dataconn->new->close '
Can't use an undefined value as a symbol reference at /usr/lib/perl5/5.10.0/Net/FTP/dataconn.pm line 54.