title: check against: null vs default()?
body: <p>I want to check if a reference type is null.  I see two options (_settings is of reference type FooType):</p>
  
  <pre><code>if (_settings == default(FooType)) { ... }
  </code></pre>
  
  <p>and</p>
  
  <pre><code>if (_settings == null) { ... }
  </code></pre>
  
  <p>How do these two perform differently?</p>