When iterating over a DBCursor using standard hasNext()/next() logic, hasNext() can raise a NullPointerException when the underlying server-side cursor has been closed. This happens in my code because I wrap the DBCursor in another Iterator that provides "batching": Iterates over the DBCursor generating a list of objects instead of a single object.

I has been able to trace the issue to the following code fragments in DBApiLayer:

public boolean hasNext(){
    boolean hasNext = _cur.hasNext();
    while ( !hasNext ) {
      ....
    }
    return hasNext;
}
...
void close(){
    if (_curResult != null) {
        killCursor();
        _curResult = null;
        _cur = null;
    }
}

Please the documentation tells the hasNext() method can throw a MongoException and there are some issues that deal with this API issue.