Have get_recursive_tales to raise a verbose exception when a template field may not be retrieved.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@33752 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Form/ProxyField.py

@@ -552,6 +552,8 @@ class ProxyField(ZMIField):
       return self.get_tales(id)
     else:
       proxied_field = self.getTemplateField()
+      if proxied_field is None:
+        raise AttributeError('The proxy field %r cannot find a template field' % self)
       if proxied_field.__class__ == ProxyField:
         return proxied_field.get_recursive_tales(id)
       else: