EDITOR'S NOTE
StringToBigInt("") is 0n according to the logic in 3.1.3.1.
This is not what I would do if it were up to me, but since this library is mostly just a binding to the underlying JavaScript library, perhaps the best way forward is to leave this as-is and clarify this behaviour in the documentation?
This appears to be by design in the underlying JavaScript library (emphasis mine):
The stage 3 draft BigInt specification for ES requires this too:
This is not what I would do if it were up to me, but since this library is mostly just a binding to the underlying JavaScript library, perhaps the best way forward is to leave this as-is and clarify this behaviour in the documentation?