title: IS NOT operator in C#
body: <p>I can't find the "is not" operator in C#.
  For example I have the code below which does not work. I need to check that <code>err</code> is not of type class <code>ThreadAbortException</code>.</p>
  
  <pre><code>    catch (Exception err)
      {
          if (err is not ThreadAbortException)
          {
          }
      }
  </code></pre>