<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_error_traceback(self):
 """ Method returning traceback of error page. By default it find element with class ``error-page`` and returns text of element with class ``traceback``. You can change this method accordingly to your app. """

        try:
            error_page = self.get_elm(class_name='error-page')
            traceback = error_page.get_elm(class_name='traceback')
        except NoSuchElementException:
            pass
        else:
            return traceback.text