Well, it appears that in some circumstances, either $key, $val or possibly both can be undefined. Since that probably indicates a problem with the syntax of your input file, you should test for it:

  unless (defined($key) && defined($val)) {
    warn "Problem in input: <$index>\n";
  } else {
    $key =~ s"^\s+""g;
    $key =~ s"\s+$""g;
    $val =~ s"^\s+""g;
    $val =~ s"\s+$""g;
    $hash_ref->{$key} = $val;
  }
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