Ckeditor strips  tags CKeditor strips the &lt;i&gt; tags, and I can't find where in config.js I can put this code.

CKEDITOR.dtd.$removeEmpty['i'] = false


This is a solution for Drupal 7 and the CKEditor module.
Add an empty space - &nbsp;

&lt;i class="fa fa-drupal"&gt;&amp;nbsp;&lt;/i&gt;