Hello Eva,
The error is stating that the code is attempting to use a serializable mapping for the entityJB.Baleent basketItems List, so you might want to check out how this was set up and what is in the List. A serializable mapping means that the entire collection shoudl get serialized into single field, so both the collection and the items in the collection must be serializable. If this is what is intended, you will need to use a serializable collection type, most likely a type like ArrayList instead of an interface.
I'm sorry I don't know anything about the tutorial, so I can't be of any help in whats going wrong there.
Best Regards,
Chris
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