Aqua Data Studio 15.0.0-dev-252
Build #: 37537
Built on: 2014-Apr-25 04:30:08 PM.
Database : Mongo 2.6.
O.S: Windows 8.

1. Make connection to MongoDB and execute attached script.
2. Now launch Mongoshell and execute below given script.
    db.inventory.find(  [ { qty: { $lt: 20 } }, { sale: true } ]  )
3. You will observe that in console below given error message is displayed.
   error: {"$err" : "java.lang.NullPointerException: null"}
4. Since the syntax of query is wrong so its not executing and throwing null pointer exception. If we execute same script in Mnogo DB shell no such message is displayed.
5. Correct syntax will be
    db.inventory.find( { $or: [ { qty: { $lt: 20 } }, { sale: true } ] } )