[12.x] Resolve issue with creating event and automatic eager loading

[jackbayliss]

When eager loading automatically, when the creating event & others occur via observers, or models. I noticed during tests that relationships would be set as null when using saveMany etc- where as previously without eager loading automatically they would work.

This means tests would begin to fail.

I've added a test for this behavior & removing the HasEvent changes I've made it fails.

The logic I've added removes any relations that have been set as null before the creating event, and call the eager loading chain again meaning those relations will be set properly. Because it's the first event called (I believe) it means other events no longer suffer this too.

Perhaps there's a better way, but open to ideas.

[github-actions]

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