input: Write a function to query Twitter and retrieve the most recent tweets from a given user. The function should take the username as input and return the text of the most recent tweets. If the username is empty or invalid, the function should return an empty list.
  assert query_twitter("elonmusk")==["Tweet 1 text", "Tweet 2 text"]
  assert query_twitter("invalid_user")==[]
  assert query_twitter("")==[]
output: def query_twitter(username):
      if not username:
          return []
      # Assuming we have a function or API call to get tweets
      tweets = get_tweets(username)  # Placeholder for actual API call
      if not tweets:
          return []
      return [tweet['text'] for tweet in tweets]