Under an installment lease agreement, a lessee may reject any delivery that is nonconforming if the nonconformity substantially impairs the value of that delivery and cannot be cured or the nonconformity is a defect in the required documents; but if the nonconformity does not fall within subsection (2) and the lessor or the supplier gives adequate assurance of its cure, the lessee must accept that delivery. Whenever nonconformity or default with respect to one or more deliveries substantially impairs the value of the installment lease contract as a whole there is a default with respect to the whole. But, the aggrieved party reinstates the installment lease contract as a whole if the aggrieved party accepts a nonconforming delivery without seasonably notifying of cancellation or brings an action with respect only to past deliveries or demands performance as to future deliveries.