Ferlane enters into a five-year contract with a carrier for the transport of a specified volume of goods by railcars. The contract specifies the type of railcars, but for each journey the carrier chooses the railcars used from a large pool available nearby; it can replace them at any time without Ferlane's consent, and this flexibility allows it to optimise the use of its pool at low cost. Between journeys, the railcars stay at the carrier's sites. What conclusion should be reached?