Customers cannot make new Orders after Xpath constrain on order entity

I would like to have customers to only be able to see their own orders. The advice i had was to put in the access rule of the entity order a xpath constrain.  After reading the documentation on access rules this looked fine to me: [MyFirstModule.Order_Customer='[%CurrentUser%]'] However because of this customers cannot make new orders, i get these errors: An error has occurred while handling the request. [User 'demo_Customer' with session id '510b4d82-62f2-4a9a-b7c2-805924f9975d' and roles 'Customer'] java.lang.IllegalArgumentException: requirement failed: mxObject should not be null.   this is because when I want to open the order_overview page he is not going into the microflow anymore that creates a new order. However I cannot find a solution to this problem.  
1 answers

Which entity is used for the Demo_Customer user?

If it is the default account, then the Customer does not exist. Thus the Xpath returns false => No order(s) for the current user.