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The excuse of impossibility in contracts for the sale of goods is controlled by the appropriate section of the Uniform Commercial Code, G. L. c. 106, § 2-615. 

'Excuse by Failure of Presupposed Conditions.

'Except so far as a seller may have assumed a greater obligation and subject to the preceding section on substituted performance

'(a) Delay in delivery or non-delivery in whole or in part by a seller who complies with paragraphs (b) and (c) is not a breach of his duty under a contract for sale if performance as agreed has been made impracticable by the occurrence of ...