Do not raise an error if the comment text is None.

CHANGES.txt

@@ -4,7 +4,8 @@ Changelog
 2.1.2 (unreleased)
 ------------------
 
-- nothing.
+- Do not raise an error if the comment text is None.
+  [timo]
 
 
 2.1.1 (2011-11-24)

plone/app/discussion/comment.py

@@ -138,6 +138,8 @@ class Comment(CatalogAware, WorkflowAware, DynamicType, Traversable,
             settings = registry.forInterface(IDiscussionSettings, check=False)
             sourceMimetype = settings.text_transform
         text = self.text
+        if text is None:
+            return ''
         if isinstance(text, unicode):
             text = text.encode('utf8')
         return transforms.convertTo(targetMimetype,