“ In any event, we think it appropriate that the question of local law should be answered by the courts of the District before this Court is called upon to answer it, or to consider the application and effect of the second part of Rule 17 (b) in an action in debt brought in the District of Columbia against an unincorporated labor union. There are cogent reasons why this Court should not undertake to decide questions of local law without the aid of some expression of the views of judges of the local courts who are familiar with the intricacies and trends of local law and practice. ”

“ Brown v. United States, 276 U.S. 134, 141, 48 S.Ct. 288, 289, 72 L.Ed. 500; People of Puerto Rico v. Russell & Co., 288 U.S. 476, 480 482, 483, 484, 53 S.Ct. 447, 448, 449, 450, 77 L.Ed. 903; Moffat Tunnel League v. ”