code: public <E> List<E> unmodifiable(List<E> input)
      {
          if (input == null) {
              return null;
          }
          return Collections.unmodifiableList(input);
      }
docs: Returns an unmodifiable view of the specified list.
  
  @param <E> the type of the elements in the list
  @param input the list to wrap in an unmodifiable bridge
  @return an unmodifiable view of the list