Do not assign enumerable schema to object #256

lib/schema.js

@@ -183,7 +183,7 @@ Schema.prototype.define = function defineClass(className, properties, settings)
             return new ModelConstructor(data);
         }
         AbstractClass.call(this, data);
-        this.schema = schema || this.constructor.schema;
+        hiddenProperty(this, 'schema', schema || this.constructor.schema);
     };
 
     hiddenProperty(NewClass, 'schema', schema);