Task/fix null response error

[nebHailemariam]

Handles cases where the Gorse server returns a null response for GetRecommend(string userId) by returning null instead of throwing an exception, allowing users to manage null responses more flexibly. Additionally, adds a constructor to the GorseException class to pass the error message to the base Exception class, ensuring the error is displayed. Previously, GorseException lacked a constructor to initialize the base message.

Additionally, replace the status code check with a more robust check.

// Checks only for HTTP 200 if (response.StatusCode != HttpStatusCode.OK)

// Checks succes if (!response.IsSuccessStatusCode) { throw new GorseException { StatusCode = response.StatusCode, Message = response.Content };

[zhenghaoz]

LGTM