Fix potential crash

tournaments/models/tournament.py

@@ -475,7 +475,7 @@ class Tournament(models.Model):
                     key=lambda m: (
                         m.round.index,       # Sort by Round index first
                         m.round.get_depth(),
-                        m.name, # Then by Round depth
+                        m.name or '', # Then by Round depth, using empty string if name is None
                     )
                 )
                 group = self.create_match_group('Matchs de classement', ranking_matches)