code: public void addGLL( GLLSentence gll ) {
          try {
              if (gll.isValid())
                  position = gll.getPosition();
          } catch (Exception e) {
              // ignore it, this should be handled in the isValid,
              // if an exception is thrown, we can't deal with it here.
          }
      }
docs: Method to add a new {@link GLLSentence}.
  
  @param gll the sentence to add.