Major Description
When calling addMutation or addMutations on a MockBatchWriter, the updates stored in the mutation are iterated over then committed in the MockTable class.
When this occurs in the TabletServerBatchWriter (eventually called from the BatchWriterImpl), however, the mutation size is first checked and if the mutation size is 0, an IllegalArgumentException is thrown.
In practice, if you have code that tries to submit an empty mutation to a BatchWriter, it will fail and throw an exception in the real world, but this will not be caught in tests against MockAccumulo.