✅ How to return null in a generalized method?

public static async Task<T?> ResultResponse<T>(this HttpResponseMessage result, string message)
    {
        if (!result.IsSuccessStatusCode) return null;
        string responseBody = await result.Content.ReadAsStringAsync();
        return responseBody
            .Contains(message,
                StringComparison.CurrentCultureIgnoreCase)
            ? null
            : JsonConvert.DeserializeObject<T>(responseBody);
    }