Major Description
Calling SegmentWriter.writeMap(base, changes) with changes containing mappings to null (meaning to remove the respective key) can result in a NPE if base doesn't contain that key.
I came across this while working on the PersistedCompactionMap in OAK-2862. I had to add an extra check for above case as otherwise I'd occasionally hit said NPE.
Need yet to extract a proper test case.