As others have said, List::Util is a core module, so you should be able to rely on it being available (assuming you don't need to support Perl older than 5.7.3). If not, it's really easy to implement it yourself:

sub uniq (@) {
  my %seen;
  my $undef;
  my @uniq = grep defined($_) ? !$seen{$_}++ : !$undef++, @_;
  @uniq;
}
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