Acme Investment has entered into a contact to purchase an office building from Good Office Corp. The sales price is all cash to the seller. Prior to the closing, Acme assigns its rights under the contact to Zebra Investments. Zebra shows up at the closing with the cash to buy the office building. Zebra is a competitor of Good Office, and Good Office does not want to sell the office building to Zebra. Can Good Office refuse to sell to Zebra? What issues may affect your answer?