feat(animations): allow @.disabled property to work without an expression (#18713)

PR Close #18713

packages/compiler/src/template_parser/binding_parser.ts

@@ -218,7 +218,7 @@ 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));
   }