feat(animations): allow @.disabled property to work without an expression

packages/compiler/src/template_parser/binding_parser.ts

@@ -219,7 +219,7 @@ export class BindingParser {
     // This will occur when a @trigger is not paired with an expression.
     // For animations it is valid to not have an expression since */void
     // states will be applied by angular when the element is attached/detached
-    const ast = this._parseBinding(expression || 'null', false, sourceSpan);
+    const ast = this._parseBinding(expression || 'undefined', false, sourceSpan);
     targetMatchableAttrs.push([name, ast.source !]);
     targetProps.push(new BoundProperty(name, ast, BoundPropertyType.ANIMATION, sourceSpan));
   }

packages/core/test/animation/animation_integration_spec.ts

@@ -2691,6 +2691,43 @@ export function main() {
              fixture.detectChanges();
              expect(getLog().length).toEqual(1);
            });
+
+        it('should treat the property as true when the expression is missing', () => {
+          @Component({
+            selector: 'parent-cmp',
+            animations: [
+              trigger(
+                  'myAnimation',
+                  [
+                    transition(
+                        '* => go',
+                        [
+                          style({opacity: 0}),
+                          animate(500, style({opacity: 1})),
+                        ]),
+                  ]),
+            ],
+            template: `
+              <div @.disabled>
+                <div [@myAnimation]="exp"></div>
+              </div>
+                `
+          })
+          class Cmp {
+            exp = '';
+          }
+
+          TestBed.configureTestingModule({declarations: [Cmp]});
+
+          const fixture = TestBed.createComponent(Cmp);
+          const cmp = fixture.componentInstance;
+          fixture.detectChanges();
+          resetLog();
+
+          cmp.exp = 'go';
+          fixture.detectChanges();
+          expect(getLog().length).toEqual(0);
+        });
       });
     });
 

packages/platform-browser/animations/src/animation_renderer.ts

@@ -206,7 +206,8 @@ export class AnimationRenderer extends BaseAnimationRenderer implements Renderer
   setProperty(el: any, name: string, value: any): void {
     if (name.charAt(0) == ANIMATION_PREFIX) {
       if (name.charAt(1) == '.' && name == DISABLE_ANIMATIONS_FLAG) {
-        this.disableAnimations(el, !!value);
+        value = value === undefined ? true : !!value;
+        this.disableAnimations(el, value as boolean);
       } else {
         this.engine.process(this.namespaceId, el, name.substr(1), value);
       }