#nullable enable 

​

using System;

class Address 

{

    public string? Building; 

    public string Street = string.Empty;  // avoids that not in use warning you get.. 

    public string City = string.Empty; 

    public string Region = string.Empty; 

}

​

public class Program

{

    public static void Main()

    {

        var address = new Address();

        address.Building = null; 

        address.Street =  null; // cannot convert null literal to null ref type.. leave empty to fix. 

        address.City = "London"; 

        address.Region = null; 

    }

}

​

​

//to enable in a local project: 

/* 

<Project Sdk="Microsoft.NET.Sdk">

<PropertyGroup>

<OutputType>Exe</OutputType> 

<TargetFramework>netcoreapp3.0</TargetFramework> 

<Nullable>enable</Nullable> /// THIS ONE!!! 

</ProjectGroup>

</Project> 

​

​

​

*/