@@ -418,7 +418,8 @@ def generic_recursive_equality_test(a, b, class_history):
     else:
         # NOTE: The call may need to be adapted if other objects implementing a __getstate__
         # with required argument(s) are passed to this function.
-        dict_a = a.__getstate__(a) if inspect.isclass(a) else a.__getstate__()
+        # For a class that has no instance __dict__ and no __slots__, the default state is None
+        dict_a = a.__getstate__(a) if inspect.isclass(a) else a.__getstate__() or dict()
     dict_b = b.__dict__
     for key in dict_a:
         assert key in dict_b, f"Did not pickle {key}"