foreach my $field (@fields) {
  my $value = param($field);
  $value =~ s/^\s+//;
  $value =~ s/\s+$//;
  next if $value eq "";
  # construct SQL or otherwise work with $value
}

##</code><code>##

my %good_params =
    map { $_ => $params{$_} }
    grep { $params{$_} ne ""}
    keys %params;