In the case of Hutton v, Warren, the Court of Exchequer held that a lease of agriculture land must be read subjects to the custom of the locality that the tenant was bound to observe a certain course of husbandry and he was entitled to all allowance for seed and labour on quitting the land. Baron Parke observed thus: "lt has long been settled that in commercial transactions extrinsic evidence of custom and usage is admissible to annex incidents to written contracts in matters with respect to which they are silent......... This has been done upon the principle of presumption that in such transactions the parties did not mean to express in writing the whole of the contract by which they intended to be bound, but to contract with reference to these known usage." a. Explain the case and to which topic it is related?