title: Google API 1.8.1 - Google Drive document commenter's PermissionId/EmailAddress
body: <p>I have a very simple code:</p>
  
  <pre><code>...
  DriveService service = new DriveService(initializer);
  
  CommentList comments = service.Comments.List(fileId).Execute();
  ...
  </code></pre>
  
  <p>As a result I get a list of comments (comments.Items property), in each comment there is an Author property having populated only "DisplayName" and a "Picture" properties.
  "PermissionId" property is a null and I am confused how to retrieve permissionId or email address of the commenter?</p>
  
  <p>Thanks in advance.</p>