MongoDB Query 判断为空 取值为空的时间

if (!string.IsNullOrEmpty(STATES))
            {
                DateTime? dtnull = null;
                //Return
                if (STATES == "Return")
                {

                    //list.Add(Query.NE("ReturnTime", ((MongoDB.Bson.BsonValue)DateTime.Now).AsBsonNull));
                    list.Add(Query.NE("ReturnTime", ((MongoDB.Bson.BsonValue)dtnull).AsNullableDateTime));
                    //list.Add(Query.Null
                }
                //Not Return
                if (STATES == "Not Return")
                {
                    //list.Add(Query.EQ("ReturnTime", (Nullable<DateTime>)null));
                    list.Add(Query.EQ("ReturnTime", ((MongoDB.Bson.BsonValue)dtnull).AsNullableDateTime));
                }

            }

list.Add(Query.NE("ReturnTime", null));

list.Add(Query.NE("ReturnTime", “null”));

都是没用的

要用里面的

自带属性

AsNullableDateTime 获取