NPE when adding or editing comments via the "More Actions" menu

Steps to reproduce:

• go to the wiki home page
• click the "More Actions" menu, then on "Comments"
• add a comment and notice how the comment input and the "Preview" and "Add Comment" buttons are disabled (see "AddComment.png")
• refresh the page and see that the comment has been added but that the add comment input is still displayed (see "CommentAdded.png")
• click the pen icon in order to edit the comment - the add comment input is still there (see "EditComment.png")
• click on "Save Comment" and see how the input and the buttons are disabled (see "CommentEdited.png")

The logs show a NPE exception (see "logs.txt").