input: Write a function to take in two strings as input and output a list of all the words in both strings. If the input strings are 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("Hello world", "")==["Hello", "world"]
  assert string_to_list("", "Programming is fun")==["Programming", "is", "fun"]
  assert string_to_list("", "")==[]
output: def string_to_list(str1, str2):
      if not str1 and not str2:
          return []
      words = []
      if str1:
          words.extend(str1.split())
      if str2:
          words.extend(str2.split())
      return words