In this release 5.0.69, you will be able to control whether the Cashier can close orders without assigning a customer to the order, or not. 

Based on a new setting in the Console > Cashier Settings. You can enable the "Require Customer Info Before Closing Any Order". If enabled, this will prevent the cashier from proceeding to the payment page without assigning a customer. The customer selection screen will appear for the cashier to select a customer and proceed with payment.