PhysicsDebugNode undefined

Hi, I’m using cocos creator to create a simple physics game.
the cc.PhysicsDebugNode return undefined!
anyway to debug physics body ?
here is my code
cc.log(cc.PhysicsDebugNode);// return undefined in the browser-console
cc.PhysicsDebugNode.create(this.space);
this._debugNode = cc.PhysicsDebugNode.create( this.space );
this._debugNode.visible=true;
this.addChild( this._debugNode );
Thanks