ok should never be null

[Frank LaRosa]

I agree wholeheartedly with the spirit of this message. But I don't know what's causing it or what I need to do to resolve the problem. Any ideas?

Exception 1: ‘ok’ should never be null… java.lang.IllegalArgumentException: ‘ok’ should never be null…

at com.mongodb.CommandResult.ok(CommandResult.java:41)
at com.mongodb.DBCollection.findAndModify(DBCollection.java:377)
at com.mongodb.DBCollection.findAndModify(DBCollection.java:404)

[Bryan]

 If this is a sharded system, it is most likely an issue where after a migration the getLastError (WriteConcern.SAFE) call goes to the config servers and not the shards which took the write. We have a fix for this situation in V2.1.2