pdo: handle None cob_id gracefully in __repr__

Author: stoicfeats

canopen/pdo/base.py

@@ -229,7 +229,8 @@ def __init__(self, pdo_node, com_record, map_array):
         self._task = None
 
     def __repr__(self) -> str:
-        return f"<{type(self).__qualname__} {self.name!r} at COB-ID 0x{self.cob_id:X}>"
+        cob = f"0x{self.cob_id:X}" if self.cob_id is not None else "Unassigned"
+        return f"<{type(self).__qualname__} {self.name!r} at COB-ID {cob}>"
 
     def __getitem_by_index(self, value):
         valid_values = []