Woodson Walker and Associates leased computer equipment from Park Ryan Leasing. The lease said nothing about assignment. Park Ryan then assigned the lease to TCB as security for a loan. Park Ryan defaulted on its loan, and Walker failed to make several payments on the lease. TCB sued Walker for the lease payments. Was the assignment valid, given the fact that the original lease made no mention of it? If the assignment was valid, may Walker raise defenses against TCB that it could have raised against Park Ryan?