input: Write a function to process Twitter data and visually summarize it using matplotlib. The function should take the Twitter data as input, which includes fields like tweet author, date of tweet, text, number of likes, and number of retweets. The output should be visual summaries in the form of bar charts for the number of tweets per author, the number of likes per tweet, and the number of retweets per tweet.
  assert twitter_summary([['Alice', '2022-01-01', 'Hello', 10, 5], ['Bob', '2022-01-02', 'Hi', 5, 3], ['Alice', '2022-01-03', 'Hi Again', 15, 7]])==None
  assert twitter_summary([['Charlie', '2022-01-04', 'Hello There', 20, 10]])==None
  assert twitter_summary([])==None
output: def twitter_summary(data):
      if not data:
          return None
      
      authors = [tweet[0] for tweet in data]
      likes = [tweet[3] for tweet in data]
      retweets = [tweet[4] for tweet in data]
      
      import matplotlib.pyplot as plt
      
      plt.figure(figsize=(15, 5))
      
      plt.subplot(1, 3, 1)
      author_counts = {author: authors.count(author) for author in set(authors)}
      plt.bar(author_counts.keys(), author_counts.values())
      plt.title('Number of Tweets per Author')
      plt.xlabel('Author')
      plt.ylabel('Number of Tweets')
      
      plt.subplot(1, 3, 2)
      plt.bar(range(len(likes)), likes)
      plt.title('Number of Likes per Tweet')
      plt.xlabel('Tweet Index')
      plt.ylabel('Number of Likes')
      
      plt.subplot(1, 3, 3)
      plt.bar(range(len(retweets)), retweets)
      plt.title('Number of Retweets per Tweet')
      plt.xlabel('Tweet Index')
      plt.ylabel('Number of Retweets')
      
      plt.tight_layout()
      plt.show()
      
      return None