Using grep on undefined array

[Andrew Beverley]

Hi,

Could someone please explain to me why the following outputs an empty
string rather than "*"?

get();
sub get($)
{   my $fields = shift;
    my @fields = grep $_ ne 'domain', @$fields;
    my $select_fields = $fields ? join(',', map { 'users.' . $_ } @fields) : '*';
    print "$select_fields\n";
}

I would have expected $fields to remain undefined, but it seems to be
turning into an empty array during the grep.

I've discovered that I can make it work by conditionally declaring
@fields (with "if $fields"), but I'd still like to know what's going on
here.

Thanks,

Andy