Set default to avoid `includes` being called on `undefined`

dist/converse.js

@@ -67110,7 +67110,8 @@ _converse_core__WEBPACK_IMPORTED_MODULE_6__["default"].plugins.add('converse-muc
     });
     _converse.ChatRoomOccupant = Backbone.Model.extend({
       defaults: {
-        'show': 'offline'
+        'show': 'offline',
+        'states': []
       },
 
       initialize(attributes) {

src/headless/converse-muc.js

@@ -1099,7 +1099,8 @@ converse.plugins.add('converse-muc', {
         _converse.ChatRoomOccupant = Backbone.Model.extend({
 
             defaults: {
-                'show': 'offline'
+                'show': 'offline',
+                'states': []
             },
 
             initialize (attributes) {