test empty too for version restriction too

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@12018 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/BusinessTemplate.py

@@ -4536,7 +4536,7 @@ Business Template is a set of definitions, such as skins, portal types and categ
           installed_bt = self.portal_templates.getInstalledBusinessTemplate(dependency)
           if (not self.portal_templates.IsOneProviderInstalled(dependency)) \
              and ((installed_bt is None) \
-                  or (version_restriction is not None and 
+                  or (version_restriction not in (None, '') and 
                      (not self.portal_templates.compareVersionStrings(installed_bt.getVersion(), version_restriction)))):
             missing_dep_list.append((dependency, version_restriction or ''))
       if len(missing_dep_list) != 0: