public class WithString
        {
            [BsonIgnoreIfNull]
            public string S { get; set; }
        }

        [Test]
        public void StringIsNullOrEmptyShouldTestIgnoredNulls()
        {
        
            var a = new WithString() {S = "ooo"};
            var b = new WithString() {S = ""};
            var c = new WithString() { };

            collection.Insert(a);
            collection.Insert(b);
            collection.Insert(c);

            var query = from t in collection.AsQueryable()
                        where string.IsNullOrEmpty(t.S)
                        select t;

            var translated = MongoQueryTranslator.Translate(query);
            var mongoQuery = ((SelectQuery)translated).BuildQuery();
            Debug.WriteLine(mongoQuery.ToString());

            var results = query.ToList();
            Assert.That(results.Count, Is.EqualTo(2));
        }