[Zope] How to exclude Confera messages?

[Loren Stafford]

Based on code others have suggested on this list, I've implemented a
"breadcrumbs" navigation stack method. The code is below. It works well
unless I navigate into a Confera message object, where it fails with the
Traceback included below.

I don't understand why it fails, but that's OK. I don't really need for it
to put Confera messages on the breadcrumbs stack.

What I would like to know is: How can I detect and exclude a Confera
message? Can anyone help me out?

-- Thanks
-- Loren

<!--#call "REQUEST.set('dirs', [])"-->
<!--#in expr="PARENTS" skip_unauthorized-->
  <!--#call "dirs.insert(0, id)"-->
<!--#/in-->

<!--#in dirs-->
<!--#with "_[_['sequence-item']]"-->

  <!--#if "_['sequence-start']"-->
<a href="/">Home</a>
  <!--#else-->
     <!--#if "_['sequence-end']"-->
&nbsp;&gt;&nbsp;<!--#var title_or_id-->
     <!--#else-->
 &gt;&nbsp;<a href="<!--#var absolute_url-->"><!--#var id--></a>
     <!--#/if-->
  <!--#/if-->

<!--#/with-->
<!--#/in-->

Sorry, an error occurred.

Traceback (innermost last):
  File lib/python/ZPublisher/Publish.py, line 877, in publish_module
  File lib/python/ZPublisher/Publish.py, line 590, in publish
    (Info: //Discuss/934833119/index_html)
  File lib/python/Products/Confera/Confera.py, line 541, in index_html
  File lib/python/OFS/DTMLMethod.py, line 155, in __call__
    (Object: message_html)
  File lib/python/OFS/DTMLMethod.py, line 151, in __call__
    (Object: message_html)
  File lib/python/DocumentTemplate/DT_String.py, line 513, in __call__
    (Object: message_html)
  File lib/python/OFS/DTMLMethod.py, line 147, in __call__
    (Object: standard_html_header)
  File lib/python/DocumentTemplate/DT_String.py, line 513, in __call__
    (Object: standard_html_header)
  File lib/python/OFS/DTMLMethod.py, line 147, in __call__
    (Object: breadcrumbs)
  File lib/python/DocumentTemplate/DT_String.py, line 513, in __call__
    (Object: breadcrumbs)
  File lib/python/DocumentTemplate/DT_In.py, line 683, in renderwob
    (Object: dirs)
  File lib/python/DocumentTemplate/DT_With.py, line 133, in render
    (Object: _[_['sequence-item']])
  File lib/python/DocumentTemplate/DT_Util.py, line 266, in eval
    (Object: _[_['sequence-item']])
  File <string>, line 0, in ?
  File lib/python/DocumentTemplate/DT_Util.py, line 150, in careful_getitem
KeyError: Sorry, an error occured