DataReplicator::_onOplogFetchFinish has this code:

    BSONElement tsElem(doc->getField("ts"));
    while(tsElem.eoo() || doc != docs.rend()) {
        tsElem =  (doc++)->getField("ts");
    }

    if (!tsElem.eoo()) {
        _lastTimestampFetched = tsElem.timestamp();
    } else {
        warning() <<
                "Did not find a 'ts' timestamp field in any of the fetched documents";
    }

1 - It seems like the while(tsElem.eoo()) condition would prevent the else/warning block from ever being executed because the code can't advance until tsElem.eoo() == false.

2 - The or condition in while() seems like it could allow doc to advance past docs.rend() when no docs have a 'ts' field. (Should it just be an && condition instead?)