实例化Django模型会引发TypeError：isinstance（）arg 2必须是类和类型的类，类型或元组

I have an existing, functional Django application that has been running in DEBUG mode for the last several months. When I change the site to run in production mode, I begin getting the following Exception emails sent to me when I hit a specific view that tries to create a new Referral model object.I have an existing, functional Django applicati