(a) A rental agreement may provide for the payment by the tenant of the costs of a suit, for unpaid rent, and reasonable attorney's fees not in excess of twenty-five per cent of the unpaid rent after default and referral to an attorney not a salaried employee of the landlord or the landlord's assignee.
(b) A rental agreement may further provide that reasonable attorney's fees and costs may be awarded to the prevailing party in all other matters arising under this chapter.
(c) A provision in violation of this section is unenforceable.