input: Write a function to identify the longest word in a given sentence. If the sentence is empty, return an empty string. If there are multiple words with the same maximum length, return the first one found.
  assert find_longest_word("The rain in Spain stays mainly in the plain.") == "mainly"
  assert find_longest_word("Python is a great programming language") == "programming"
  assert find_longest_word("") == ""
  assert find_longest_word("Short words are nice") == "words"
  assert find_longest_word("Single") == "Single"
output: def find_longest_word(sentence):
      if not sentence:
          return ""
      words = sentence.split()
      longest_word = ""
      for word in words:
          if len(word) > len(longest_word):
              longest_word = word
      return longest_word