When there is an express agreement for the payment of the sum of money secured contained in the mortgage or any separate instrument, the court shall direct in the decree of foreclosure that the balance due on the mortgage, and costs which may remain unsatisfied after the sale of the mortgaged premises, shall be satisfied from any property of the mortgage debtor: PROVIDED, HOWEVER, That in all cases where the mortgagee or other owner of such mortgage has expressly waived any right to a deficiency judgment in the complaint, as provided by RCW 6.23.020, there shall be no such judgment for deficiency, and the remedy of the mortgagee or other owner of the mortgage shall be confined to the sale of the property mortgaged.