code: public static <T> ImmutableList<T> asUniquedList(Iterable<T> items) {
      return ImmutableSet.copyOf(items).asList();
    }
docs: A copy of the input as an {@link com.google.common.collect.ImmutableList} which respects
  iteration order, but where only the first occurrence of each element is kept. No input items
  may be {@code null}.