fix(angular1_router): ngLink should not throw an error if routeParams are undefined (#8460)

If routeParams are undefined, no href attribute should be rendered. This matches the behaviour of ngHref.

modules/angular1_router/src/ng_outlet.ts

@@ -213,6 +213,10 @@ function ngLinkDirective($rootRouter, $parse) {
     let link = attrs.ngLink || '';
 
     function getLink(params) {
+      if (!params) {
+        return;
+      }
+
       navigationInstruction = router.generate(params);
 
       scope.$watch(function() { return router.isRouteActive(navigationInstruction); },

modules/angular1_router/test/ng_link_spec.js

@@ -140,6 +140,18 @@ describe('ngLink', function () {
       navigateTo('/');
       expect(elt.find('a').attr('class')).toBe('ng-link-active');
     });
+
+    it('should not add a href if link attributes are undefined', function () {
+      setup({baseHref: baseHref, html5Mode: html5Mode, hashPrefix: hashPrefix});
+      configureRouter([
+        { path: '/a', component: 'oneCmp' },
+        { path: '/b', component: 'twoCmp', name: 'Two' }
+      ]);
+
+      var elt = compile('<a ng-link="something.undefined">link</a> | outer { <div ng-outlet></div> }');
+      navigateTo('/a');
+      expect(elt.find('a').hasAttr('href')).toBeFalsy();
+    });
   }
 
   function registerComponent(name, template, controller) {