not vs no

Contracts must not require a party to perform an act which is impossible. If performance of an obligation is impossible, the contract obligating the party to perform the impossible act may not be enforceable. That which makes the act impossible must be no fault of the breaching party.

Which is correct?
That which makes the act impossible must be no fault of the breaching party.
That which makes the act impossible must not be the fault of the breaching party.
Thanks