code: public void setErrorListener(ErrorListener listener) throws IllegalArgumentException
    {
      if (listener == null) 
        throw new IllegalArgumentException(XSLMessages.createXPATHMessage(XPATHErrorResources.ER_NULL_ERROR_HANDLER, null)); //"Null error handler");
      m_errorListener = listener;
    }
docs: Set the ErrorListener where errors and warnings are to be reported.
  
  @param listener A non-null ErrorListener reference.