(b) That's right. The parties to a contract are free to decide the nature and extent of their obligations and the courts will seek to give effect to their intentions. But when deciding what has been agreed, the courts apply an objective approach rather than a subjective one. This means that the courts do not ask what the parties actually (that is, subjectively) intended their agreement to mean. Instead, the courts ask what a third party would reasonably understand the terms to mean. In the circumstances of this case, a third party would not reasonably have thought that the phrase 'during the lease' would exclude a long period of notice.
The courts' objective approach means that each party to a contract should, at the time of contracting, evaluate the proposed terms objectively, and if the objective meaning does not accord with what they intend, they should ensure that a more accurate expression of the agreement is formulated.