fixed so that it does not raise exception when sthg is None

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@9853 20353a03-c40f-0410-a6d1-a30d3c3de9de

bt5/erp5_dms/SkinTemplateItem/portal_skins/erp5_dms/DMSFile_view/my_contributor_list.xml

@@ -317,7 +317,7 @@
       <dictionary>
         <item>
             <key> <string>_text</string> </key>
-            <value> <string>python: here.getContributorTitleList()+here.getContributorNameList()</string> </value>
+            <value> <string>python: (here.getContributorTitleList() or [])+(here.getContributorNameList() or [])</string> </value>
         </item>
       </dictionary>
     </pickle>