docs: public String convertToPrefixLength() throws AddressStringException {
  		IPAddress address = toAddress();
  		Integer prefix;
  		if(address == null) {
  			if(isPrefixOnly()) {
  				prefix = getNetworkPrefixLength();
  			} else {
  				return null;
  			}
  		} else {
  			prefix = address.getBlockMaskPrefixLength(true);
  			if(prefix == null) {
  				return null;
  			}
  		}
  		return IPAddressSegment.toUnsignedString(prefix, 10, 
  				new StringBuilder(IPAddressSegment.toUnsignedStringLength(prefix, 10) + 1).append(IPAddress.PREFIX_LEN_SEPARATOR)).toString();
  	}