title: Unable to check null for header value in request
body: <p>I tried to get header value like below -</p>
  
  <pre><code>IEnumerable&lt;string&gt; headerValues = request.Headers.GetValues("MyCustomerId");
  var id = headerValues.FirstOrDefault();
  </code></pre>
  
  <p>If header value is null or not present it is throwing error - <code>InvalidOperationException</code></p>
  
  <p>The null check for <code>GetValues</code> doesn't serve any value as it will never return null. If the header doesn't exist you will get an InvalidOperationException</p>
  
  <p>Any trick to do so?</p>