The Migration of User tasks into the flow node field looks like it can throw an NPE. The nightly job fails. Originally I thought it was how we extracted the event counts, so I merged https://github.com/camunda/camunda-optimize/pull/3481. However, even after that we now see the NPE. The new task logging gives a nice hint as to where the problem lies, so hopefully this is something that can be resolved. 

Upgrade failure logs: https://stage.ci.optimize.camunda.cloud/job/upgrade-performance-large-static-dataset/188/artifact/qa/upgrade-tests/target/update-schema-optimize-upgrade.log

The tests for this migration don't cover very many use cases, so perhaps we could uncover the issue if we added more diverse process instances in terms of their properties, as well as instances from multiple indices, to the tests