Enable Nullable Reference Types feature

[m-wild]

We should use the C# 8.0 feature Nullable Reference Types to prevent Null Reference Exceptions.

https://docs.microsoft.com/en-us/dotnet/csharp/nullable-references

[domca25101]

Hi, I'd like to dig into this issue. Could you give me a bit of guidance and possibly assign this to me?

[m-wild]

My advice for this one would be to

• first enable nullable reference types <Nullable>enable</Nullable> in the project file.
• set the language version to latest <LangVersion>latest</LangVersion>
• I would then begin looking through the AsyncAPI specification (https://www.asyncapi.com/docs/specifications/2.0.0) at each type and for any property which is OPTIONAL add the ? to allow it to be null.
• For non-optional properties, I would add a constructor which checks for null.

e.g. If we look at the Info object
https://www.asyncapi.com/docs/specifications/2.0.0#infoObject
Title and Version are required. All others can be null.

public class Info
{
    public Info(string title, string version)
    {
        Title = title ?? throw new ArgumentNullException(nameof(title));
        Version = version ?? throw new ArgumentNullException(nameof(version));
    }

    [JsonPropertyName("title")]
    public string Title { get; }

    [JsonPropertyName("version")]
    public string Version { get; }

    [JsonPropertyName("description")]
    public string? Description { get; set; }

    [JsonPropertyName("termsOfService")]
    public string? TermsOfService { get; set; }

    [JsonPropertyName("contact")]
    public Contact? Contact { get; set; }

    [JsonPropertyName("license")]
    public License? License { get; set; }
}

[dgnaegi]

Hi @domca25101 , are you still working on this one? I would be interested as well

[domca25101]

Hi @dgnaegi, yes I am working on it.

[domca25101]

Hi, I have encountered a couple issues that I need a bit of help with:

1. As you described in the comment above, I need to add required properties to the constructor, which checks for nulls. In case of AsyncApi object, however, Info property is required, but adding it as a required parameter of constructor necessitates changes to all its instantiations and I'm having trouble figuring some of them out.

2. There are some cases, where presence of null check is not necessary from context, but if null check is omitted, there will be warning asking for one. Should I use arbitrary null check in this case or just suppress the warning?

[m-wild]

For (2), I would add the check.

For (1), I will review the code when I am back from holiday and reply.

[m-wild]

Closing as not needed for now.