Recovery of improvement expenses paid by occupier

Notwithstanding anything contained in section 501, when the occupier of any premises pays any installment of improvement expenses, he shall, subject to any agreement to the contrary, if any, between himself and the owner of such premises, be entitled to deduct the amount of such installment from the rent payable by him to such owner or to recover such amount from such owner in pursuance of any order of a court of competent jurisdiction.