What is the legal ruling regarding the phrase "the empty is full" in painting work, which means painting the door along with the wall for the same wage, given the homeowner's consent?

There is no harm in what you do if there is mutual consent between you and the homeowner to not subtract the area of the door when calculating the area of the wall to be painted, for Allah Almighty says: "O you who have believed, do not consume one another's wealth unjustly but only [in lawful] business by mutual consent." This also applies if it has become common practice.