Support default values for detached styles

src/style_manager/model/Layers.js

@@ -1,3 +1,4 @@
+import { isUndefined } from 'underscore';
 import Backbone from 'backbone';
 import Layer from './Layer';
 
@@ -110,11 +111,13 @@ export default Backbone.Collection.extend({
     return result.join(this.getSeparator());
   },
 
-  getPropertyValues(property) {
+  getPropertyValues(property, defValue) {
     const result = [];
     this.each(layer => {
       const value = layer.getPropertyValue(property);
-      value && result.push(value);
+      value
+        ? result.push(value)
+        : !isUndefined(defValue) && result.push(defValue);
     });
     return result.join(', ');
   }

src/style_manager/view/PropertyStackView.js

@@ -277,7 +277,8 @@ export default PropertyCompositeView.extend({
 
         if (model.get('detached')) {
           const subProp = subModel.get('property');
-          const values = self.getLayers().getPropertyValues(subProp);
+          const defVal = subModel.getDefaultValue();
+          const values = self.getLayers().getPropertyValues(subProp, defVal);
           view.updateTargetStyle(values, null, opt);
         } else {
           // Update only if there is an actual update (to avoid changes for computed styles)