Misleading exception when referencing a list of unmergeable entities

Summary

I have the following configuration which produces exceptions which should not happen in this way:

• RecordType A references LIST<B>
• The Identifiable of B consists of is_referenced_by: A, and some properties of B.
• There is data for one A record and two B records.
  • The two B records have equal registered identifiables, but they cannot be merged due to other reference properties which are different.

This leads to an exception in

# line 803 in crawl.py
                identifiable = self.identifiableAdapter.get_identifiable(
                    record,
                    referencing_entities=referencing_entities[id(record)])

because referencing_entities does not contain id(record)of the firstB` record (any more?). Therefore, the exception complains about a missing referencing entity:

NotImplementedError('Could not find referencing entities...

Expected Behavior

There should be an exception about the merge conflict, not about missing referencing entities.

Actual Behavior

This error

Steps to Reproduce the Problem

I will write a short test for this

Specifications

• Version: Current dev branch, plus some unrelated minor changes.
• Platform: Which operating system, which other relevant software versions?

Possible fixes

Do you have ideas how the issue can be resolved?