Improve error messages for invalid basket content

[Thomas-Gelf]

Expected Behavior

Errors related to invalid (binary) data should be easy to track down.

Current Behavior

When a basket cannot be encoded (read: transformed into JSON), this has historically been because of non-UTF8-characters (like binary UUIDs) slipping through. Such errors are hard to track down, as the message shows no hint pointing to the object causing this problem

Possible Solution

When an encoding error occurs, let's iterate over every single object, pick the first culprit one and enrich the message with related information.

[Thomas-Gelf]

[Thomas-Gelf]

Formerly, this looked as follows: