Any court of probate shall, before proving or disapproving any last will and testament, or codicil thereto, hold a hearing thereon, of which notice, either public or personal or both, as the court may deem best, has been given to all parties known to be interested in the estate, unless all parties so interested sign and file in court a written waiver of such notice, or unless the court, for cause shown, dispenses with such notice. The finding by any such court that the estate is not more than sufficient to pay the expenses of administration and of the funeral and last sickness shall be sufficient cause to dispense with such notice.