Discord.Net/docs/guides/commands/samples/customresult_extended.cs

public class MyCustomResult : RuntimeResult
{
    public MyCustomResult(CommandError? error, string reason) : base(error, reason)
    {
    }
    public static MyCustomResult FromError(string reason) =>
        new MyCustomResult(CommandError.Unsuccessful, reason);
    public static MyCustomResult FromSuccess(string reason = null) =>
        new MyCustomResult(null, reason);
}