// original
        function checkMassSignAbility(){
            var keys = Object.keys($scope.selectedTransactions)
                .filter(function(key){return $scope.selectedTransactions[key].checked});
            if (!keys.length)
                return false;
            return keys.every(function(key){
                var row = $scope.selectedTransactions[key];
                if (!row)
                    return false;
                return actions.sign.visible(row);
            });
        }

// fixed
        function checkMassSignAbility() {
                return $scope.selectedTransactions.length > 0
                   && $scope.selectedTransactions.every(actions.sign.visible);
        }