input: Write a function to implement a chatbot in Python that can provide customer support in a restaurant. The function reads a user's question from 'random_user_question.txt' and provides a random response from a predefined list of possible responses. If the file does not exist or is empty, the function should print "Question not found." without quotes.
  
  assert chatbot_response()=="We serve a variety of dishes - from salads to pizzas to steaks!"
  assert chatbot_response()=="Check out our menu for a full list of options"
  assert chatbot_response()=="Question not found."
  assert chatbot_response()=="We have a unique selection of meals - have you checked out our menu?"
output: import random
  
  def chatbot_response():
      try:
          with open('random_user_question.txt', 'r') as file:
              question = file.read().strip()
              if not question:
                  return "Question not found."
              responses = [
                  "We serve a variety of dishes - from salads to pizzas to steaks!",
                  "Check out our menu for a full list of options",
                  "We have a unique selection of meals - have you checked out our menu?"
              ]
              return random.choice(responses)
      except FileNotFoundError:
          return "Question not found."