code: public static boolean isEmpty(final Label label) {
          for (Label.MapFieldEntry entry : label.getEntryList()) {
              for (String value : entry.getValueList()) {
                  if (!value.isEmpty()) {
                      return false;
                  }
              }
          }
          return true;
      }
docs: Test if the label is empty. This means that every label list for every
  languageCode is empty or that it only contains empty string.
  
  @param label the label type which is tested
  
  @return if the label type is empty as explained above