Section 1. An executor, administrator, guardian or conservator, or a trustee required by law to give bond to a judge of probate, shall render an account relative to the estate in his hands at least once a year and at such other times as shall be required by the court, until his trust is fulfilled; but the court may at his request excuse him from rendering an account in any year, if satisfied that it is not necessary or expedient that it should be rendered.