Rental income

I own a property which is being rented by a company, dell. I will renew the lease on the property next month for a period of 12 months. My question is, somebody has offered to buy the lease for a period of 12 months for a lumpsum payment (discounted) and he will receive the rent from the tennant for a period of only 12 months. First question, is this allowed, legally. Second question, if yes, what is the tax treatment?