Performing a search in which data must be sorted and you insert "" as key you get a poor error message.

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MongoClient mongo = new MongoClient(new ServerAddress(host, port),
credentialList);
DB mongodb = mongo.getDB(DB_NAME)
DBCollection table = mongodb.getCollection(TABLE_NAME);
DBCursor cursor = table.find();
BasicDBObject orderBy = new BasicDBObject() ;
orderBy.put("", 1);
cursor.sort(orderBy);

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com.mongodb.MongoException: assertion d:\slave\windows_64bit_v2.4\mongo\src\mongo\db\../bson/bsonobjbuilder.h:92
at com.mongodb.MongoException.parse(MongoException.java:82)
at com.mongodb.DBApiLayer$MyCollection.__find(DBApiLayer.java:292)
at com.mongodb.DBApiLayer$MyCollection.__find(DBApiLayer.java:273)
at com.mongodb.DBCursor._check(DBCursor.java:368)
at com.mongodb.DBCursor._hasNext(DBCursor.java:459)
at com.mongodb.DBCursor.hasNext(DBCursor.java:484)