input: Write a function to take in two strings as input and output a list of all the words in both strings. If either string is empty, return an empty list.
  assert string_to_list("I want to make a difference", "The journey to success is long")==['I', 'want', 'to', 'make', 'a', 'difference', 'The', 'journey', 'to', 'success', 'is', 'long']
  assert string_to_list("", "The journey to success is long")==[]
  assert string_to_list("I want to make a difference", "")==['I', 'want', 'to', 'make', 'a', 'difference']
  assert string_to_list("", "")==[]
output: def string_to_list(str1, str2):
      if not str1 or not str2:
          return []
      return str1.split() + str2.split()