getMore command behind DBCursor.hasNext appears to require that a primary exists in the replica-set somewhere. It does not require a connection to it (AFAIK) but it insists that a primary be nominated.

Reproduction:
1. Set up a 3 node replica-set (PSS).
2. Kill 2 nodes.
3. Run Java client with a readPreference of secondary and perform a simple query.
4. Call hasNext on the returned cursor until 101 results.
5. Stack trace follows:

Caused by: com.mongodb.MongoException: can't find a master
at com.mongodb.DBTCPConnector.checkMaster(DBTCPConnector.java:517)
at com.mongodb.DBTCPConnector.innerCall(DBTCPConnector.java:236)
at com.mongodb.DBTCPConnector.call(DBTCPConnector.java:216)
at com.mongodb.DBTCPConnector.call(DBTCPConnector.java:184)
at com.mongodb.DBApiLayer$Result._advance(DBApiLayer.java:427)
at com.mongodb.DBApiLayer$Result.hasNext(DBApiLayer.java:396)
at com.mongodb.DBCursor._hasNext(DBCursor.java:464)
at com.mongodb.DBCursor.hasNext(DBCursor.java:484)

It would seem the first DBTCPConnnector.call passes "null" as a readPref to the counterpart which dutifully passes that through to DBTCPConnector.innerCall which defaults to primary (because null readpref) and the getMore helper has constructed an OutMessage instance with no readpref either. Thus checkMaster is erroneously called with "true" for "failIfNoMaster".