code: @VisibleForTesting
  	public static boolean isValid(String nip) {
  		String normalizedNip = normalizeNip(nip);
  		if (normalizedNip.length() != NIP_LENGTH) {
  			return false;
  		}
  		try {
  			int checksum = calculateChecksum(normalizedNip);
  			return checksum == normalizedNip.charAt(CHECKSUM_CHAR_INDEX) - '0';
  		} catch (NumberFormatException e) {
  			LOG.debug(format("Invalid nip %s", nip), e);
  			return false;
  		}
  	}
docs: TODO: Move to separate module