return set;
      }

      @Override
      public boolean add(@ParametricNullness E element) {
        throw new UnsupportedOperationException();
      }

      @Override
      public boolean addAll(Collection<? extends E> es) {
        throw new UnsupportedOperationException();
      }
    };
  }

  private static <E extends @Nullable Object> SortedSet<E> removeOnlySortedSet(