fix: define if it exists in teh params

src/openapi_python_generator/language_converters/python/templates/httpx.jinja2

@@ -1,8 +1,12 @@
 {%  if async_client %}async {% endif %}def {{ operation_id }}(self, {{ params }} api_config_override : Optional[APIConfig] = None) -> {% if return_type.type is none or return_type.type.converted_type is none %}None{% else %}{{ return_type.type.converted_type}}{% endif %}:
     api_config = api_config_override if api_config_override else self.config
     x_interaction_id=self.set_interaction_id(x_interaction_id)
+{% if 'client_id' in params %}
     client_id= client_id or api_config.client_id
+{% endif %}
+{% if 'client_secret' in params %}
     client_secret= client_secret or api_config.client_secret
+{% endif %}
 
     base_path = self.config.base_path
     path = f'{{ path_name }}'