Rasa error with slot, how can i fix that?

Question

I have this in actions.py :

from rasa_sdk import Action from rasa_sdk.events import SlotSet from langdetect import detect

class LanguageDetectionAction(Action): def name(self): return "language_detection_action"

def run(self, dispatcher, tracker, domain):
    user_input = tracker.latest_message.get("text")
    detected_language = detect(user_input)
    print(tracker.get_slot("detected_language"))
    dispatcher.utter_message("joke")
    return SlotSet("detected_language", detected_language)

and that's my domain:

responses: utter_greet: - condition: - type: slot name: detected_language value: "en" text: "Thank you for signing up! What do you need help with?" - condition: - type: slot name: detected_language value: "ar" text: "مرحبا"

and thats my story :

• story: Language-based Greeting steps:
  • intent: greet
  • action: language_detection_action
  • action: utter_greet

I need this code to work