What is the effect of a mistake as to the existence of the subject matter? Which of the following is correct?

Where a contract is made for something yet to come into existence, then until the subject matter actually comes into being, there is no contract between the parties

Mistake as to the existence of the subject matter does not change an agreement, each party takes the risk that the goods may or may not be in existence, all obligations stay intact

Where there is a mistake as to existence of the subject matter, the goods no longer exist, then the agreement is ended since an agreement assumes that the contract can be fulfilled

If the goods were in existence at the time of making the contract, the contract remains enforceable, irrespective of whether the goods disappear, alternatively if the goods were never in existence then the contract is not enforceable