function scheduleRender() {
    if (renderScheduled) return;
    renderScheduled = true;
    $scope.$$postDigest(function() {
      renderScheduled = false;
      self.ngModelCtrl.$render();
    });
  }
@ngdoc method
@name select.SelectController#$isEmptyOptionSelected

@description

Returns `true` if the select element has an empty option and this empty option is currently
selected. Returns `false` if the select element has no empty option or it is not selected.