Calendar provider crashes with NPE when `eventStatus` is UPDATEd to `null`, even when it's already `null`

[rfc2822]

We have a workaround for updating non-null eventStatus to null: in that case we delete/re-create instead of updating.

However we currently don't handle the case when eventStatus is already null and then explicitly updated to null. However that case crashes with the same NPE too.