sub validate {
  my @params = @_;
  my @warning;

  for ( @params ) {
    my %h = ( missing => $_);
    push (@warning, \%h ) unless $c->param($_); 
  }
  if ( @warning ) {
    print $c->header;
    my $template = HTML::Template->new(filename => './templates/warning.html');
    #don't use die $! while testing HTML::Template has it's own error handling
    $template->param( warnings => \@warning );
    print $template->output();
    exit;
  }
}