MongoDb query array with null values

Question

I have objects in my collection that look like:

{ MyArray:[null, "some value", null] }

I want to query those objects that have a null value as an array element. The query

db.collection.find({"MyArray":null})

does not work, it seems to find only the objects with MyArray being null, e.g.

{ MyArray:null }

How do I need to define my query?

EDIT: Please see one of my real objects:

{
        "_id" : BinData(3,"ch9PrWveqU6niB6FGVhIOg=="),
        "PeerGroup" : "male",
        "ProductId" : BinData(3,"weRiKOtXEUSDZHkGHLcwzw=="),
        "CategoryIds" : [
                BinData(3,"BXzpwVQozECLaPkJy26t6Q=="),
                BinData(3,"ox303ZeM50KelvoUbPBJ8Q=="),
                BinData(3,"26ziaY+G9UKMyjmtVkkhcg=="),
                BinData(3,"D2X8vObte0eJHNcDfp2HBw==")
        ],
        "ShopId" : BinData(3,"ZdfPmrlKR0GkLPC4djJuKw=="),
        "BrandId" : BinData(3,"kCHyuyLvgECxPF1nxwr7qQ=="),
        "Created" : ISODate("2012-08-24T07:42:12.416Z"),
        "LastActivity" : ISODate("2013-01-14T19:38:11.776Z"),
        "Price" : 129.9,
        "Sale" : false,
        "Rating" : 11.057340703605368,
        "RatingTimed" : 0.05670431130054035,
        "Available" : null,
        "FreeDelivery" : null,
        "Attrs" : [
                null,
                null,
                null,
                null
        ]
}

And then I query by:

db.collection.find({"Attrs":null})

which yields no results.

Answer 1

In order to find documents with arrays, with null elements please run:

db.collection.find({"keyWithArray":{$elemMatch:{"$in":[null], "$exists":true}}})

According to safaribooksonline proper null matching is performed using $in (because you cannot use $eq with null). Also, comparing with null:

{"something":null}

will match documents with "something" field set to null and every document which does not have "something" field at all. Thus we have to make sure the key exists using $exists.