Merge billing items when merging people or companies Report

Currently, we can register time on a ticket which is registered as a billing item.
These time registrations can later be exported for billing to the customers.

When we merge people or companies (often duplicates) this billing items are not merged together, which means that they are lost for billing.
The records are still in the database, but are not linked anymore to the old user or old company.

It would be better if billing items are merged together with users or companies.