### This is a bug about a backend library, no QA needed

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### Steps to reproduce

1. Create a custom field with multiple values

2. Add multiple values (i.e. `1,2,3`)

3. Check `thing.custom_field_changes`


### What is the buggy behavior?

* Only the last value is reported as a change (changeset: `[nil, 3]`)


### What is the expected behavior?

1. The changeset should contain all new values as an array Begin of the insertion`[[],End of the insertion Begin of the deletion `[nil,End of the deletion [1,2,3]]`