Using a Site generated by the Mirium-Demo template, there is a list of existing products that are generated. Some of these products have a variant, and you will not be able to add them to the cart due to what appears to be a database error
Steps to Reproduce
These steps assume that you're using a Site based off of Mirium-Demo
1. Login as anyone
2. Go to a Commerce's Site's dashboard
3. Search for any product that uses product variances, such as Hoses or Brake Fluid
4. Choose a Package Quantity (this is actually not necessary, but it's good to ensure that this is a not a variable) and then click on "Add to Cart"
Expected: It will be added to your cart
Actual: A red banner appears with the error No CPInstance exists with the primary key 0
Since I have only found this to be an issue with demo data, this may be a lower priority, but if we're passing this demo out to customers, then we should definitely fix this since it will look bad if our own demo data doesn't work.