input: Write a function to find the longest word in a given sentence. If there are multiple words with the same longest length, return the first one encountered. 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 programming is fun") == "programming"
  assert find_longest_word("Short words here") == "words"
  assert find_longest_word("") == ""
  assert find_longest_word("   ") == ""
output: def find_longest_word(sentence):
      if not sentence.strip():
          return ""
      words = sentence.split()
      return max(words, key=len)