can't delete variables

src/Umbraco.Web.UI.Client/src/views/propertyeditors/grid/dialogs/layoutconfig.controller.js

@@ -28,7 +28,7 @@ angular.module("umbraco")
     		    if(toggle){
     		        collection = [];
     		    }else{
-    		        delete collection;
+    		        collection = null;
     		    }
     		};
 

src/Umbraco.Web.UI.Client/src/views/propertyeditors/grid/dialogs/rowconfig.controller.js

@@ -27,7 +27,7 @@ function RowConfigController($scope) {
             collection = [];
         }
         else {
-            delete collection;
+            collection = null;
         }
     };
 

src/Umbraco.Web.UI.Client/src/views/propertyeditors/grid/grid.prevalues.controller.js

@@ -189,7 +189,7 @@ angular.module("umbraco")
             if(toggle){
                 collection = [];
             }else{
-                delete collection;
+                collection = null;
             }
         };
 

src/Umbraco.Web.UI.Client/src/views/propertyeditors/tags/tags.controller.js

@@ -207,7 +207,7 @@ angular.module("umbraco")
                 tagsHound.clearPrefetchCache();
                 tagsHound.clearRemoteCache();
                 $element.find('.tags-' + $scope.model.alias).typeahead('destroy');
-                delete tagsHound;
+                tagsHound = null;
             });
 
         });