erp5_web: make sure link has value

bt5/erp5_web/DocumentTemplateItem/portal_components/document.erp5.ReplaceRelativeUrlTextDocument.py

@@ -35,11 +35,12 @@ class ReplaceRelativeUrlTextDocument(TextDocument, object):
           # By conversion, first letter of reference should be upper case
           # To be more sure of what to replace
           # erp5-Howto
-          if new_link[0].isupper() or new_link.startswith('erp5-') or new_link.startswith('user-') or \
-             new_link.startswith('slapos-') or new_link.startswith('vifib-') or new_link.startswith('osoe-') or \
-             new_link.startswith('developer-') or new_link.startswith('slapOS'):
-            transformed_link_tag = link_tag.replace(link, '%s/%s' % (web_section_url, new_link), 1)
-            html = html.replace(link_tag, transformed_link_tag)
+          if new_link:
+            if new_link[0].isupper() or new_link.startswith('erp5-') or new_link.startswith('user-') or \
+               new_link.startswith('slapos-') or new_link.startswith('vifib-') or new_link.startswith('osoe-') or \
+               new_link.startswith('developer-') or new_link.startswith('slapOS'):
+              transformed_link_tag = link_tag.replace(link, '%s/%s' % (web_section_url, new_link), 1)
+              html = html.replace(link_tag, transformed_link_tag)
 
     for img_tag in re.findall(match_img_tag, html):
       src = re.search(match_img_src, img_tag)