Hi. I'd like to create a component that extends Phaser.Group so that I can add elements to it, and then add the entire component to anywhere in my game. But, it seems like I'm misunderstanding something. This is my code: GameName.Entity = function(game) { Phaser.Group.call(this, game);};GameName.Entity.prototype = Object.create(Phaser.Group.prototype);GameName.Entity.prototype.constructor = GameName.Entity;GameName.SomeStage = function(game) {};GameName.SomeStage.prototype = { var entity = new GameName.Entity(this.game); // Throws: Uncaught TypeError: Cannot set property '_iPrev' of undefined this.game.add.existing(entity); }};What am I doing wrong?