(a) In Baltimore City, a liquidated damages clause or penalty clause in a residential lease is not enforceable. If a tenant fails or refuses to take possession of or vacates the dwelling unit before the end of his term, the tenant is liable to the landlord for loss of rent caused by the termination or [two] 6 months' rent, whichever is less, in addition to the cost of repairing damage to the premises which may have been caused by an act or omission of the tenant.