FIX: id replacement

Summary

Entities that have no ID (because they were not yet inserted) are not replaced by None.

Test Environment

There is an existing integration test

Check List for the Author

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• All automated tests pass
• Reference related issues #12 (closed)
• Up-to-date CHANGELOG.md (or not necessary)
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?

For further good practices have a look at our review guidelines.