diff --git a/gramps/gen/plug/docbackend/docbackend.py b/gramps/gen/plug/docbackend/docbackend.py
index 4c6d0c6e5..f10a4068f 100644
--- a/gramps/gen/plug/docbackend/docbackend.py
+++ b/gramps/gen/plug/docbackend/docbackend.py
@@ -222,6 +222,8 @@ class DocBackend(object):
             return self.format_link(s_tag.value)
         typeval = int(s_tag.name)
         s_tagvalue = s_tag.value
+        if s_tagvalue is None:
+            return None
         tag_name = None
         if tagtype.STYLE_TYPE[typeval] == bool:
             return self.STYLETAG_MARKUP[self.STYLETYPE_MAP[typeval]]