Undefined or null for AngularJS

Question

When I write watch handling functions I check newVal param on undefined and null. Why does AngularJS have such a behavior, but doesn't have particular utility method? So there is angular.isUndefined but not angular.isUndefinedOrNull. It isn't hard to implement that by hand but how extend angular to have that function in each controller? Tnx.

Edit:

The example:

$scope.$watch("model", function(newVal) {
    if (angular.isUndefined(newVal) || newVal == null) return;
    // do somethings with newVal
}

Is it common accepted practice to handle such a way?

Edit 2:

The JSFiddle example (http://jsfiddle.net/ubA9r/):

<div ng-app="App">
  <div ng-controller="MainCtrl"> 
      <select ng-model="model" ng-options="m for m in models">
          <option value="" class="ng-binding">Choose model</option>
      </select>
      {{model}}
  </div>
</div>

var app = angular.module("App", []);

var MainCtrl = function($scope) {
    $scope.models = ['Apple', 'Banana'];
    $scope.$watch("model", function(newVal) {
        console.log(newVal);
    });
};

Answer 1

You can always add it exactly for your application

angular.isUndefinedOrNull = function(val) {
    return angular.isUndefined(val) || val === null 
}