Currently this will error with `need to specify the desired max chunk size` on an empty collection because mongos runs the splitVector command with force:true on the shard which uses the dataSize as the maxChunkSizeBytes  variable. But the dataSize for an empty collection will be zero so it returns a generic error about maxChunkSizeBytes even though that's not something the user of the split command has control over. 

https://github.com/mongodb/mongo/blob/r6.0.3/src/mongo/db/s/split_vector.cpp#L130-L137