Pages with emoticons created in older versions are not displayed, nor can be edited

Issue Summary

Pages with emoticons created in older versions of Confluence (at least 3 or older) simply display error com.atlassian.confluence.content.render.xhtml.XhtmlException: Unmarshaller encountered element with missing shortcut and no content, in version 6.15.6 or later.

If Collaborative Editing is On, editing the page will display a pop-up:

Steps to Reproduce

1. Setup an instance with Confluence 6.15.6 and install the Confluence Source Editor app;
2. Create a page and add two  emoticons to it;
3. Edit the page with the Source Editor;
4. Replace the second <ac:emoticon ac:name="tick"/> with:

   <img class="emoticon" src="<base-url>/images/icons/emoticons/check.png" alt="" width="16" height="16" border="0" />

   Insert the instance's Base URL in the text above.

1. Press Apply;

Expected Results

The page is displayed, showing one  emoticon and text (unknown emoticon).

Actual Results

The editor shows the error com.atlassian.confluence.content.render.xhtml.XhtmlException: Unmarshaller encountered element with missing shortcut

Opening the Source Editor again will not display previous storage format.

Notes

This happens when the emoticons are stored in the page in a format similar to:

<img class="emoticon" src="<base-url>/images/icons/emoticons/check.png" alt="" width="16" height="16" border="0" />

We could only verify that this format was used up to version 3. In case of a customer having such pages created in a old version, will see the problem after an upgrade to 6.15.6 or later.

Running the same steps in version 6.15.4 does not reproduce the error.

Workaround

The page's storage format can be changed using the Confluence Source Editor app. Search all occurrences of class="emoticon" and replace it with one of the following values (depending on the actual emoticon to be displayed):

	class="emoticon emoticon-smile"
	class="emoticon emoticon-sad"
	class="emoticon emoticon-cheeky"
	class="emoticon emoticon-laugh"
	class="emoticon emoticon-wink"
	class="emoticon emoticon-thumbs-up"
	class="emoticon emoticon-thumbs-down"
	class="emoticon emoticon-information"
	class="emoticon emoticon-tick"
	class="emoticon emoticon-cross"
	class="emoticon emoticon-warning"
	class="emoticon emoticon-plus"
	class="emoticon emoticon-minus"
	class="emoticon emoticon-question"
	class="emoticon emoticon-light-on"
	class="emoticon emoticon-light-off"
	class="emoticon emoticon-yellow-star"
	class="emoticon emoticon-red-star"
	class="emoticon emoticon-green-star"
	class="emoticon emoticon-blue-star"

This will allow the page to be displayed and edited.

Alternate Workaround

Disable the Confluence Hipchat Emoticons Plugin