A recent change from append to addition made it possible to have yet another exception type.

Author: Roland Hedberg

src/saml2/entity.py

@@ -341,7 +341,7 @@ def sign(self, msg, mid=None, to_sign=None, sign_prepare=False):
 
         try:
             to_sign += [(class_name(msg), mid)]
-        except AttributeError:
+        except (AttributeError, TypeError):
             to_sign = [(class_name(msg), mid)]
 
         logger.info("REQUEST: %s" % msg)