HttpClient null warning in C# 9+

Question

I've just migrated an .NET3.1 application to .NET6 (I am using VS 2022) and I noticed that they've introduced some constraints related to nullable types. I fixed all my code to follow best practices, but not sure how to go about this issue:

When creating a new HttpClient instance it returns a nullable HttpClient type (code is executed inside a Polly retry policy):

   public async Task<List<InterestedParty>> GetInterestedPartiesAsync()
    {
        return await _retryPolicy.ExecuteAsync(async () =>
        {
            using var client = new HttpClient()
            const string endpoint = "my-endpoint";
            var url = $"{endpoint}/test";

            var response = await client.GetAsync(url);
            response.EnsureSuccessStatusCode();

            var jsonString = await response.Content.ReadAsStringAsync();
            return JsonConvert.DeserializeObject<List<InterestedParty>>(jsonString);
        });
    }

The compiler is complaining about a possible null reference return. I know I could suppress the warning by using:

#pragma warning disable CS8603 // Possible null reference return.

but I don't think it's the best solution.

Any other suggestions? Thank you.

Answer 1

The issue itself it's not related to HttpClient as I thought in the beginning.

The return type of the method it's Task<List> and inside the using statement I was returning

JsonConvert.DeserializeObject<List<InterestedParty>>(jsonString); Indeed, the deserialized object can be null, so one solution would be add the "null forgiving" operator (!) at the end:

   public async Task<List<InterestedParty>> GetInterestedPartiesAsync()
    {
        return await _retryPolicy.ExecuteAsync(async () =>
        {
            using var client = new HttpClient();
            const string endpoint = "my-endpoint";
            var url = $"{endpoint}/test";

            var response = await client.GetAsync(url);
            response.EnsureSuccessStatusCode();

            var jsonString = await response.Content.ReadAsStringAsync();
            return JsonConvert.DeserializeObject<List<InterestedParty>>(jsonString)!;
        });
    }

Another better suggestion would be :

  public async Task<IEnumerable<InterestedParty>> GetInterestedPartiesAsync()
{
    return await _retryPolicy.ExecuteAsync(async () =>
    {
        using var client = new HttpClient();
        const string endpoint = "my-endpoint";
        var url = $"{endpoint}/test";

        var response = await client.GetAsync(url);
        response.EnsureSuccessStatusCode();

        var jsonString = await response.Content.ReadAsStringAsync();
        return JsonConvert.DeserializeObject<List<InterestedParty>>(jsonString) ??
               Enumerable.Empty<InterestedParty>();
    });
}

Thanks @JeroenMostert and @DavidG for your suggestion.