When will the federal courts interpret a copyright transfer agreement based on state law rather than federal law?

It is well settled that state law rules of contract construction govern the interpretation of copyright transfer agreements, notwithstanding the federal statutory source of the rights at issue. Graham v. James , 144 F.3d 229, 237 (2d Cir. 1998). Accordingly, to the extent that state law follows the parol evidence rule, federal courts should apply that rule in interpreting copyright transfer agreements. We must thus consider which state's rules of contract construction apply here.