WriteBatch method will not write data to the DB if the list passed in only has one entry.

[ldhasson]

The WriteBatch method loops over the data passed in but only writes in batches (thus the name). The problem is that if a single element is passed in, the main loop only adds an entry to the batch job and exits: after the loop, there is a catched to flush any incomplete batch, but that checks for index != 0

  if (index != 0 && (index + 1) % batchSize == 0)

That check will simply cause it to not execute if the list passed in only add 1 element.