The AutoSplitVector command chooses split points by scanning the documents in a collection and choosing the new split point to be the shard key values of the first document that makes the chunk too large. If this document has any of the shard key values unset or set to null, this will result in the new chunk having a max key that doesn't have the right number of key values. We should modify the AutoSplitVector so that it never chooses null values as a split point.