@Override
      public boolean contains(@CheckForNull Object o) {
        return Collections2.safeContains(submap.entrySet(), o);
      }

      @Override
      public boolean remove(@CheckForNull Object o) {
        if (!contains(o)) {
          return false;
        }
        // requireNonNull is safe because of the contains check.
        Entry<?, ?> entry = requireNonNull((Entry<?, ?>) o);

      @Override
      public boolean contains(@CheckForNull Object o) {
        return Collections2.safeContains(submap.entrySet(), o);
      }

      @Override
      public boolean remove(@CheckForNull Object o) {
        if (!contains(o)) {
          return false;
        }
        // requireNonNull is safe because of the contains check.
        Entry<?, ?> entry = requireNonNull((Entry<?, ?>) o);