question: public static _Fields findByThriftId ( int fieldId ) { switch ( fieldId ) { case 1 : return CLIENT_APPKEY ; case 2 : return TRACE_ID ; case 3 : return SPAN_ID ; case 4 : return ROOT_MESSAGE_ID ; case 5 : return CURRENT_MESSAGE_ID ; case 6 : return SERVER_MESSAGE_ID ; case 7 : return DEBUG ; case 8 : return SAMPLE ; case 9 : return CLIENT_IP ; default : return null ; } }
target:  Find the _Fields constant that matches fieldId, or null if its not found.