def GroupsGet(self, parameters = None, group_id = -1):
        """
            Retrieve groups from CommonSense, according to parameters, or by group id. 
            If successful, result can be obtained by a call to getResponse(), and should be a json string.
            
            @param parameters (dictionary) (optional) - Dictionary containing the parameters for the api-call.
            @param group_id (int) (optional) - Id of the group to retrieve details from.
            
            @return (boolean) - Boolean indicating whether GroupsGet was successful.
        """
        if parameters is None and group_id == -1:
            self.__error__ = "no arguments"
            return False

        url = ''
        if group_id is -1:
            url = '/groups.json'
        else:
            url = '/groups/{0}.json'.format(group_id)

        if self.__SenseApiCall__(url, 'GET', parameters = parameters):
            return True
        else:
            self.__error__ = "api call unsuccessful"
            return False