code: function requestUnfinishedPastUnitsOfPrivateChains(arrChains, onDone) {
  	if (!onDone)
  		onDone = function () {
  		};
  
  	privatePayment.findUnfinishedPastUnitsOfPrivateChains(arrChains, true, function (arrUnits) {
  		if (arrUnits.length === 0)
  			return onDone();
  		breadcrumbs.add(arrUnits.length + " unfinished past units of private chains");
  		requestProofsOfJoints(arrUnits, onDone);
  	});
  }
docs: light only