input: Write a function to visually summarize the Twitter data. The function should process the Twitter data to extract the relevant data fields and plot the tweet authors, number of likes, and number of retweets using matplotlib. If the Twitter data is empty, the function should display a message indicating that no data is available for visualization.
  
  def summarize_twitter_data(twitter_data):
      if not twitter_data:
          print("No data available for visualization.")
          return
      
      authors = []
      num_tweets = []
      num_likes = []
      num_retweets = []
      
      for tweet in twitter_data:
          authors.append(tweet['author'])
          num_tweets.append(tweet['date_of_tweet'])
          num_likes.append(tweet['likes'])
          num_retweets.append(tweet['retweets'])
      
      import matplotlib.pyplot as plt
      
      # Plot the tweet authors
      plt.xlabel('Tweet Authors')
      plt.ylabel('Number of tweets')
      plt.title('Tweet Author Summary')
      plt.bar(authors, num_tweets)
      plt.show()
      
      # Plot the number of likes
      plt.xlabel('Tweets')
      plt.ylabel('Number of Likes')
      plt.title('Number of Likes Summary')
      plt.bar(tweets, num_likes)
      plt.show()
      
      # Plot the number of retweets
      plt.xlabel('Tweets')
      plt.ylabel('Number of Retweets')
      plt.title('Number of Retweets Summary')
      plt.bar(tweets, num_retweets)
      plt.show()
  
  assert summarize_twitter_data([{'author': 'User1', 'date_of_tweet': 1, 'likes': 10, 'retweets': 5}, {'author': 'User2', 'date_of_tweet': 2, 'likes': 20, 'retweets': 10}]) == None
  assert summarize_twitter_data([]) == None
output: def summarize_twitter_data(twitter_data):
      if not twitter_data:
          print("No data available for visualization.")
          return
      
      authors = []
      num_tweets = []
      num_likes = []
      num_retweets = []
      
      for tweet in twitter_data:
          authors.append(tweet['author'])
          num_tweets.append(tweet['date_of_tweet'])
          num_likes.append(tweet['likes'])
          num_retweets.append(tweet['retweets'])
      
      import matplotlib.pyplot as plt
      
      # Plot the tweet authors
      plt.xlabel('Tweet Authors')
      plt.ylabel('Number of tweets')
      plt.title('Tweet Author Summary')
      plt.bar(authors, num_tweets)
      plt.show()
      
      # Plot the number of likes
      plt.xlabel('Tweets')
      plt.ylabel('Number of Likes')
      plt.title('Number of Likes Summary')
      plt.bar(authors, num_likes)
      plt.show()
      
      # Plot the number of retweets
      plt.xlabel('Tweets')
      plt.ylabel('Number of Retweets')
      plt.title('Number of Retweets Summary')
      plt.bar(authors, num_retweets)
      plt.show()