@Override
  public boolean clear() throws QueryException {
    throw new UnsupportedOperationException("Not yet implemented");
  }
Remove an index entry for a RegionEntry when invalidate/destroy is called OR new index key is
inserted for the RegionEntry. In case of update only forward map is cleared of old key and NO
update is performed on reverse map as that has already been done during
{@link HashIndex#basicAddMapping(Object, RegionEntry)}.

@param key - Index key.
@param entry RegionEntry for which is being updated by user.
@param updateReverseMap true only when RegionEntry is invalidated/destroyed.
geode-core/src/main/java/org/apache/geode/cache/query/internal/index/HashIndex.java