title: What is the double question mark equals sign (??=) in C#?
body: <p>I've been seeing statements like this a lot:</p>
  <pre class="lang-cs prettyprint-override"><code>int? a = 5;
  
  //...other code
  
  a ??= 10;
  </code></pre>
  <p>What does the <code>??=</code> mean in the second line? I've seen <code>??</code> used for null coalescing before, but I've never seen it together with an equals sign.</p>