docs: @Override
  	public Integer getPrefixLength() {
  		Integer ret = cachedPrefixLength;
  		if(ret == null) {
  			int prefix = getMinPrefixLengthForBlock();
  			if(prefix == getBitCount()) {
  				cachedPrefixLength = NO_PREFIX_LENGTH;
  				return null;
  			}
  			return cachedPrefixLength = prefix;
  		}
  		if(ret.intValue() == NO_PREFIX_LENGTH.intValue()) {
  			return null;
  		}
  		return ret;
  	}