input: Write a function to extract the non-vowel words in a sentence. If the sentence is empty then return an empty list. The function should split the sentence into words and check each word to see if it contains any vowel characters. If a word does not contain any vowel characters, it should be added to the result list. Finally, the function should return the list of non-vowel words.
  assert extract_words("This machine learning project is challenging.")==['T', 'm', 'ch', 'll', 'ng', 'pr', 'j', 'ct', 's', 'ch', 'll', 'ng']
  assert extract_words("Hello World!")==['H', 'W', 'rld']
  assert extract_words("")==[]
output: def extract_words(sentence):
      vowels = "aeiouAEIOU"
      if not sentence:
          return []
      words = sentence.split()
      non_vowel_words = [word for word in words if not any(char in vowels for char in word)]
      return non_vowel_words