docs: private int getLiteralId(String literal) throws PersistenceBrokerException
      {
          ////logger.debug("lookup: " + literal);
          try
          {
              return tags.getIdByTag(literal);
          }
          catch (NullPointerException t)
          {
              throw new MetadataException("unknown literal: '" + literal + "'",t);
          }
  
      }