title: How to use type reference nullable or how to enable it on preview in .NET Core
body: <p>My problem is that i keep having the error <strong>CS8652</strong> </p>
  
  <p>"C# The feature is currently in Preview and <em>unsupported</em>. To use Preview features, use the language version."</p>
  
  <p>By using "?" after the type to authorize the property to be null during a deserialization (i use JsonConvert if it helps, maybe there is a parameter that authorize some property to be null, but i don't really think so)</p>
  
  <pre><code>class Data
  {
      String? PropertyCanBeNull { get; set; }
  }
  </code></pre>
  
  <p>I've tried almost all i've found to resolve this error including the following  : 
      - Install Visual Studio 2019 Preview
      - Install .NET SDK for preview (and checking in CMD that it worked)
      - Modified my project property so that it use the .NET Core 3.0+ version</p>
  
  <p>I also tried to change the language version for my project, but it seems it's useless in my case.</p>
  
  <p>"When your project targets a preview framework that has a corresponding preview language version, <strong>the language version used is the preview language version</strong>."</p>
  
  <p>Source : <a href="https://docs.microsoft.com/fr-fr/dotnet/csharp/language-reference/configure-language-version" rel="nofollow noreferrer">https://docs.microsoft.com/fr-fr/dotnet/csharp/language-reference/configure-language-version</a></p>
  
  <p><strong>Answered by Dirk in comments</strong> :</p>
  
  <p>I also remember using the "?" after the type some time ago, but i'm not really sure, did they do any change to it so that it is supported only in "preview" or something ?</p>
  
  <blockquote>
    <p>Nullable value types (like int?) have been in C# for a very long time. Nullable reference types (like string?) however were introduced with C# 8.</p>
  </blockquote>