input: Write a function to identify the longest word in a given sentence. If there are multiple words with the same longest length, return any one of them. If the sentence is empty, return an empty string.
  assert find_longest_word("The rain in Spain stays mainly in the plain.") == "mainly"
  assert find_longest_word("Python is a great language for beginners and experts alike.") == "beginners"
  assert find_longest_word("Word") == "Word"
  assert find_longest_word("") == ""
  assert find_longest_word("123456789 12345 123456 123 1234567") == "123456789"
output: def find_longest_word(sentence):
      if not sentence:
          return ""
      words = sentence.split()
      longest_word = max(words, key=len)
      return longest_word