code: public static KeyGroupRange of(int startKeyGroup, int endKeyGroup) {
  		return startKeyGroup <= endKeyGroup ? new KeyGroupRange(startKeyGroup, endKeyGroup) : EMPTY_KEY_GROUP_RANGE;
  	}
docs: Factory method that also handles creation of empty key-groups.
  
  @param startKeyGroup start of the range (inclusive)
  @param endKeyGroup end of the range (inclusive)
  @return the key-group from start to end or an empty key-group range.