Where a partner has paid a premium on entering into partnership for a fixed term, and the firm is dissolved before the expiration of that term otherwise than by the death of a partner, he shall be entitled to repayment of the premium or of such part thereof as may be reasonable, regard being had to the terms upon which he became a partner and to the length of time during which he was a partner, unless--
         (a) the dissolution is mainly due to his own misconduct, or
         (b) the dissolution is in pursuance of an agreement containing no provision for the return of the premium or any part of it.