Entry<K, Collection<V>> entry = sortedMap().ceilingEntry(key);
      return (entry == null) ? null : wrapEntry(entry);
    }

    @Override
    public @Nullable K ceilingKey(@ParametricNullness K key) {
      return sortedMap().ceilingKey(key);
    }

    @Override
    public @Nullable Entry<K, Collection<V>> higherEntry(@ParametricNullness K key) {

      if (lowerEntry != null
          && lowerEntry.getValue().getUpperBound().compareTo(subRange.lowerBound) > 0) {
        lowerBound = subRange.lowerBound;
      } else {
        lowerBound = entriesByLowerBound.ceilingKey(subRange.lowerBound);
        if (lowerBound == null || lowerBound.compareTo(subRange.upperBound) >= 0) {
          throw new NoSuchElementException();
        }
      }

      Cut<K> upperBound;