In the next code block you are instructed to add the createAction to the accountController which has the parameter $request as a Request object.

public function createAction(Request $request)

I think it is easier to just include it when specifying the registerAction, but perhaps it would be  better to place a note after the createAction code mentioning that you will need to add a use statement for the Request object.

I guess the other option would be to change the line defining the createAction to something like,

public function createAction(\Symfony\Component\HttpFoundation\Request $request)