Triad Properties, Inc., owns and manages a warehouse. Ikea, a home improvement store, agrees to lease the warehouse for six years. Under the lease, Ikea is obligated to pay all of the utility costs. Two years into the term, Ikea asks Triad to modify the lease to provide that the utility costs will be split equally between them. The landlord agrees, but later decides it does not want to share the costs and refuses to pay. Is Triad bound to its agreement to share the utility costs? Why or why not?