title: Microsoft Graph API: How to tell if an attendee is a group
body: <p>I need to get events from a calendar, and find out individual users in the event.</p>
  
  <pre><code>var graphServiceClient = new GraphServiceClient(...);
  var events = graphServiceClient.Me.CalendarView.Request().GetAsync();
  // ...
  var attendee = events[0].Attendees[0];
  // Is attendee a group or user?
  // If a group, how do we expand it?
  </code></pre>