Re: An error message to understand

[tirwhan]

Does it mean that one of the @CHOICE array contents are empty?

Yes. You can avoid that warning by checking for definedness:

foreach (@CHOICE) {
    if (defined && m/2001\sCensus\sOutput\sArea/){

or

foreach (@CHOICE) {
  next if (!defined);
  if (m/2001\sCensus\sOutput\sArea/){

This uses $_ implicitly in both the definedness test and the pattern match. Often it's clearer to assign the value to a lexical variable:

for my $chosen (@CHOICE) {
    if (defined $chosen && $chosen =~ m/2001\sCensus\sOutput\sArea/){

As a further comment, usage of upper-case variable names is generally reserved for constants or perl private variables.

[Perl Mouse]

And since the pattern can never match the empty string, or 0, you could skip the define and write:

    foreach (@CHOICE) {
        if ($_ && /.../) { ... }
    }

Or:

    foreach (@CHOICE) {
        $_ or next;
        if (/.../) { ... }
    }

if all you have inside the foreach is the if statement.

[tirwhan]

I don't particularly want to argue about it but I would not approve of such a change. True, as the pattern match is now it does not make a difference, but if the pattern is ever changed it's easy to miss changing the test as well, which can introduce a subtle bug. Just checking for truth makes the code more brittle. IMO, YMMV, etc.