Add conditional to fix exception

app/views/lectures/new.coffee

@@ -13,12 +13,13 @@ $('.admin-index-button').hide()
 
 # make sure that there will always be a teacher selected
 teacherSelector = document.getElementById('lecture_teacher_id')
-sel = teacherSelector.tomselect
-sel.on 'blur', ->
-  value = sel.getValue()
-  if value == ''
-    sel.setValue(teacherSelector.dataset.current)
-  return
+if teacherSelector?
+  sel = teacherSelector.tomselect
+  sel.on 'blur', ->
+    value = sel.getValue()
+    if value == ''
+      sel.setValue(teacherSelector.dataset.current)
+   return
 
 # show the modal if the new action was triggered from course edit page
 <% if @from == 'course' %>