dunno why, sometimes RESPONSE is a None

src/App/dtml/manage_page_header.dtml

@@ -5,7 +5,7 @@
 <dtml-call "REQUEST.set('management_page_charset','utf-8')">
 </dtml-unless>
 <meta http-equiv="content-type" content="text/html;charset=&dtml-management_page_charset;" />
-<dtml-call "RESPONSE.setHeader('content-type','text/html;charset='+management_page_charset)">
+<dtml-call "RESPONSE and RESPONSE.setHeader('content-type','text/html;charset='+management_page_charset)">
 <title><dtml-if title_or_id><dtml-var title_or_id><dtml-else>Zope</dtml-if></title>
 <dtml-let ag="REQUEST.get('HTTP_USER_AGENT', '')"
      is_nav4="ag[:9] == 'Mozilla/4' and _.string.find(ag, 'MSIE') < 0"