private static <T> void addNewElements(@NotNull Collection<? super T> original, @NotNull Collection<? extends T> toAdd) {
    for (T item : toAdd) {
      if (!original.contains(item)) {
        original.add(item);
      }
    }
  }
private static <T> void addNewElements(@NotNull Collection<? super T> original, @NotNull Collection<? extends T> toAdd)