input: Write a function to identify the longest word in a given sentence. Return the longest word found in the sentence. 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("Hello world") == "Hello"
  assert find_longest_word("Python is awesome") == "awesome"
  assert find_longest_word("") == ""
  assert find_longest_word("Oneword") == "Oneword"
output: def find_longest_word(sentence):
      if not sentence:
          return ""
      words = sentence.split()
      return max(words, key=len)