FIX: Ember was raising an error without a `.set` here

FIX: Ember was raising an error without a .set here

diff --git a/app/assets/javascripts/discourse/models/store.js.es6 b/app/assets/javascripts/discourse/models/store.js.es6
index 4e6e68d..96a96f5 100644
--- a/app/assets/javascripts/discourse/models/store.js.es6
+++ b/app/assets/javascripts/discourse/models/store.js.es6
@@ -312,7 +312,7 @@ export default Ember.Object.extend({
             obj[subType] = hydrated;
             delete obj[k];
           } else {
-            obj[subType] = null;
+            Ember.set(obj, subType, null);
           }
         }
       }

GitHub sha: ad876880