Add hasValue to stack property

src/style_manager/model/PropertyStack.js

@@ -1,5 +1,6 @@
 import { keys, isUndefined } from 'underscore';
 import Property from './PropertyComposite';
+import PropertyBase from './Property';
 import Layers from './Layers';
 import { camelCase } from 'utils/mixins';
 
@@ -111,6 +112,10 @@ export default Property.extend({
     return fromStyle ? fromStyle(style) : style;
   },
 
+  hasValue(opts) {
+    return PropertyBase.prototype.hasValue.call(this, opts);
+  },
+
   /**
    * Add new layer to the stack
    * @param {Object} [props={}] Layer props