How to set and access a list slot

Rasa Open Source
1

I’m creating a custom action that accesses an API that returns a list of fun facts. I am trying to save this return in a list slot, but I can’t access it.
When I try to do this, I get the following error:

2020-10-19 01:02:50 ERROR    rasa.core.processor  - Encountered an exception while running action 'action_cat_facts'. Bot will continue, but the actions events are lost. Please check the logs of your action server for more information.
2020-10-19 01:02:50 DEBUG    rasa.core.processor  - Failed to execute custom action.
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/rasa/core/actions/action.py", line 551, in run
    json=json_body, method="post", timeout=DEFAULT_REQUEST_TIMEOUT
  File "/usr/local/lib/python3.7/site-packages/rasa/utils/endpoints.py", line 154, in request
    response.status, response.reason, await response.content.read()
rasa.utils.endpoints.ClientResponseError: 500, Internal Server Error, body='b'\n    <h1>Internal Server Error</h1>\n    <p>\n        The server encountered an internal error and cannot complete\n        your request.\n    </p>\n''

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/rasa/core/processor.py", line 650, in _run_action
    events = await action.run(output_channel, nlg, tracker, self.domain)
  File "/usr/local/lib/python3.7/site-packages/rasa/core/actions/action.py", line 574, in run
    raise Exception("Failed to execute custom action.") from e
Exception: Failed to execute custom action.
2020-10-19 01:02:50 DEBUG    rasa.core.processor  - Action 'action_cat_facts' ended with events '[]'.

domain.yml

slots:
  fatos_sobre_gatos:
    type: list
actions:
- action_cat_facts

stories.md

## fato_sobre_gato
* fatos_sobre_gatos
    - utter_fato_sobre_gatos
    - action_cat_facts

action.py

from typing import Any, Text, Dict, List
from rasa_sdk import Action, Tracker
from rasa_sdk.executor import CollectingDispatcher
from rasa_sdk.events import SlotSet
import requests

from random import randint

class ActionCatFacts(Action):
    def name(self) -> Text:
        return "action_cat_facts"

    def run(self, dispatcher, tracker, domain):

        if len(tracker.get_slot("fatos_sobre_gatos")) == 0:
            req = requests.request('GET', "https://cat-fact.herokuapp.com/facts")
            lista = []
            for n in range(3):
                lista.append(req.json()["all"][n]["text"])
            
            fato = lista[randint(0, 2)]
            
            try:
                dispatcher.utter_message("{}".format(fato))
            except ValueError:
                dispatcher.utter_message(ValueError)
            return [SlotSet("fatos_sobre_gatos", lista)]
        else:
            fato = tracker.get_slot("fatos_sobre_gatos")[randint(0, 2)]
            try:
                dispatcher.utter_message("{}".format(fato))
            except ValueError:
                dispatcher.utter_message(ValueError)
            return []
2

In the action file I was trying to get the len of a variable that had not yet been established, that is, a None variable. To fix this, I used the logical value of the slot.