'obj' was sometimes not None, but still did not have _valid_props attribute

See plotly.tests.test_core.test_errors.test_dict_path_errors.test_described_subscript_error_on_type_error for an example

Author: bmaranville

packages/python/plotly/plotly/basedatatypes.py

@@ -4777,7 +4777,7 @@ def __contains__(self, prop):
                 else:
                     return False
             else:
-                if obj is not None and p in obj._valid_props:
+                if hasattr(obj, '_valid_props') and p in obj._valid_props:
                     obj = obj[p]
                 else:
                     return False