Subject-matter of contract

   (1)  The goods which form the subject of a contract of sale may be either existing goods, owned or possessed by the seller, or future goods.

   (2)  There may be a contract for the sale of goods the acquisition of which by the seller depends upon a contingency which may or may not happen.

   (3)  Where by a contract of sale the seller purports to effect a present sale of future goods, the contract operates as an agreement to sell the goods.