We may get a NPE on calling db.getCollection("offers").update(query, updates, false, true);

Caused by: java.lang.NullPointerException: no value for: n
	at org.bson.BasicBSONObject.getInt(BasicBSONObject.java:117) ~[na:na]
	at com.mongodb.WriteResult.getN(WriteResult.java:127) ~[na:na]
	...

We see the error from time to time in our logs and don't know yet how to repoduce it.

While tracing down the issue I found another bug:
https://jira.mongodb.org/browse/SERVER-6279
However, I don't know whether they are related or not.