The logOplogEntries() function, used to format applyOps oplog entries for multi-doc transactions and batched write, fetches the lastWriteOpTime from the TransactionParticipant before writing out any oplog entries. This call is redundant because the lastWriteOptime is always null and gets set in between oplog entries in a chain of applyOps entries for a large transaction.

It should be safe to convert this TransactionParticipant::getLastWriteOpTime() to an invariant.