We currently only write the seed doc to the oplog when there are no other operations to apply. When there are operations to apply, however, we should still write this document so that other nodes that only have the seed doc in their oplog can use us as a sync source. This is safe because there is nothing special about that operation and all of the same idempotency guarantees that make the next oplog entry (which is in the oplog) safe, still apply.