[Python-experimental] Fix type error if oneof/anyof child schema is null type

modules/openapi-generator/src/main/resources/python/python-experimental/model_utils.mustache

@@ -779,7 +779,7 @@ def get_discriminator_class(model_class,
             model_class._composed_schemas.get('allOf', ())
         for cls in composed_children:
             # Check if the schema has inherited discriminators.
-            if cls.discriminator is not None:
+            if hasattr(cls, 'discriminator') and cls.discriminator is not None:
                 used_model_class = get_discriminator_class(
                                     cls, discr_name, discr_value, cls_visited)
                 if used_model_class is not None:

samples/client/petstore/python-experimental/petstore_api/model_utils.py

@@ -1046,7 +1046,7 @@ def get_discriminator_class(model_class,
             model_class._composed_schemas.get('allOf', ())
         for cls in composed_children:
             # Check if the schema has inherited discriminators.
-            if cls.discriminator is not None:
+            if hasattr(cls, 'discriminator') and cls.discriminator is not None:
                 used_model_class = get_discriminator_class(
                                     cls, discr_name, discr_value, cls_visited)
                 if used_model_class is not None:

samples/openapi3/client/petstore/python-experimental/petstore_api/model_utils.py

@@ -1046,7 +1046,7 @@ def get_discriminator_class(model_class,
             model_class._composed_schemas.get('allOf', ())
         for cls in composed_children:
             # Check if the schema has inherited discriminators.
-            if cls.discriminator is not None:
+            if hasattr(cls, 'discriminator') and cls.discriminator is not None:
                 used_model_class = get_discriminator_class(
                                     cls, discr_name, discr_value, cls_visited)
                 if used_model_class is not None: