There are a class of QS entries that QueryStatsStage::toDocument(...) skips outputting because they violate certain BSON validation constraints. Since we know whether a QS entry will violate said constraints at write-time, we can explicitly avoid writing those entries to the store. 

Perhaps this can also be extended to the other checks that lead to skipping entries at read-time.

For testing, should confirm that the store doesn't contain the entry and not just that an error was issued on the write path.