input: Write a function to scrape tweets with a particular hashtag from Twitter. The function should use the Tweepy library and print the text of each tweet. If the hashtag is empty or invalid, the function should return an error message.
  
  assert scrape_tweets("#100DaysOfCode")==True
  assert scrape_tweets("#Python")==True
  assert scrape_tweets("#")=="Invalid hashtag"
  assert scrape_tweets("")=="Invalid hashtag"
output: def scrape_tweets(hashtag):
      if not hashtag or hashtag == "#":
          return "Invalid hashtag"
      import tweepy
      auth = tweepy.OAuthHandler("API_KEY", "API_SECRET_KEY")
      auth.set_access_token("ACCESS_TOKEN", "ACCESS_TOKEN_SECRET")
      api = tweepy.API(auth)
      tweets = api.search_tweets(q=hashtag, lang="en", tweet_mode="extended")
      for tweet in tweets:
          print(tweet.full_text)
      return True