There is some background we must address before moving forward to address the statement above.
Swift v. Tyson (1842) crafted a new form of law called federal common law. The opinion was delivered by Associate Justice Joseph Story at the time.
The intent was to craft a uniform set of rules to handle negotiable instruments and other forms of commercial paper (commerce). The government of the United States never followed common law. In fact, its forms and precedences abide by Roman Civil Law and Lex Fori.
The case above was overruled in Erie R.R. v. Tompkins.
Swift had unintended consequences, particularly forum shopping for that forums standard which would be beneficial to one of the parties to a suit.
Erie eliminates the forum shopping but the remnants of this federal common law still exist with regard to commercial paper.