Ticket #5784: patch

__init__.py

@@ -468 +468 @@
             if self.null:
                 return value
             else:
-                raise validators.ValidationError, ugettext_lazy("This field cannot be null.")
+                raise validators.ValidationError, ugettext_lazy("The field '%s' cannot be null." %  self.name)
         return smart_unicode(value)
 
     def formfield(self, **kwargs):