d solely on diversity of citizenship, it would apply the ci choice-of-law rules o Texas, the state in which it sits. See Klaxon Co. Stentor Elec. Mfg. Co., 313 U.S. 487, 496, 61 S. . 1020, 85 L.Ed. 1477 (1941) . In federal question cases such as this one, however, the court must apply federal common