title: What is `Nullable<T>?`?
body: <p>I made a typo and Visual Studio didn't mark it as an error:</p>
  
  <p><code>void Method(Nullable&lt;SpriteFont&gt;? font = null) { }</code></p>
  
  <p><code>font</code> shows up as <code>SpriteFont??</code> in output. What did I just do?</p>
  
  <p><strong>UPD:</strong> Sorry, everyone, I didn't try co compile it, it just didn't show up as an error until I did. Still, it's weird that it looked as <code>Type??</code> in output.</p>
  
  <p>Furthermore <code>SpriteFont</code> is already nullable, so I was going to get an error anyway :(</p>