NullPointerException at org.grails.datastore.mapping.mongo.engine.MongoEntityPersister.checkVersion(MongoEntityPersister.java:571)

I had this issue in a real project, when storing embedded collections which contained a reference to an object in another collection. The attached integration test demonstrates the problem. However, I have not found any way to show this issue within one test. The integration test has to be run twice , without dropping the db in between. It is not sufficient to just run the test twice within one integration test - it literally has to be run twice. This may seem pretty odd, but this situation seems to occur much more often when using the mongodb plug-in within actual services. To ensure the problem is not related to any problem with the management of documents in mongo, I run the test twice within one integration test. All tests run fine within the first integration test run.