using System;

​

#nullable enable

public class Program

{

    public static void Main()

    {

        var result1 = Foo<string>(); // Works

        Console.WriteLine(result1 ?? "null");

​

        var result2 = FooNotNull<string>(); // Throws

        Console.WriteLine(result2 ?? "null");

    }

​

    public static TResponse? Foo<TResponse>()

    {

        var response = Deserialize<TResponse>();

​

        return response;

    }

​

    public static TResponse FooNotNull<TResponse>() where TResponse : notnull

    {

        var response = Foo<TResponse>();

​

        if (response is null)

        {

            throw new InvalidOperationException("Response cannot be null");

        }

​

        return response;

    }

​

    public static T? Deserialize<T>()

    {

        return default;

    }

}