Merge pull request #1826 from MITx/fix/cdodge/dont-blowup-index-if-no-course-is-None

mark stumble on case where he had a None course

cms/templates/index.html

@@ -69,7 +69,7 @@
       <article class="my-classes">
         % if user.is_active:
         <ul class="class-list">
-          %for course, url, lms_link in sorted(courses, key=lambda s: s[0].lower()):
+          %for course, url, lms_link in sorted(courses, key=lambda s: s[0].lower() if s[0] is not None else ''):
           <li>
             <a class="class-link" href="${url}" class="class-name">
               <span class="class-name">${course}</span>