title: .NET Core 3.0: Warning CS8632 The annotation for nullable reference types should only be used in code within a '#nullable' annotations context
body: <p>I get this warning when I try to use a nullable reference type like so:</p>
  
  <pre><code>using System;
  
  namespace DotNetCoreExperiment
  {
      static class Program
      {
          static void Main(string[] args)
          {
              Console.WriteLine("Hello World!");
              string? fred = null; // warning occurs here
              Console.WriteLine(fred);
          }
      }
  }
  </code></pre>
  
  <p>Why am I getting this warning and how can I fix it? I did enable <code>&lt;NullableReferenceTypes&gt;true&lt;/NullableReferenceTypes&gt;</code> in my csproj file. I don't want to do <code>#nullable enable</code> on every code file!</p>