foreach $field (qw(Data_One Second_Part)) {
   # Isolate non-empty values
   my @values = grep { ! /^\s*$/ } param($field);
   next unless @values;  # Skip if nothing available

   # Establish a header line.
   my $header = "First:";
   $header = "Second:" if $field =~ /Second_Part/;

   # Print it all. $, is the output record separator for prints
   local $, = "\n";
   print $header, @values, "\n";
}