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
     
      )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