input: Write a function to take in two strings as input and output a list of all the words in both strings. The function should split each string into a list of words using the split() method and then concatenate these two lists to form the final output list. If either of the strings is empty, the function should return the list of words from the non-empty string.
  
  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", "Python is fun") == ['Hello', 'world', 'Python', 'is', 'fun']
  assert string_to_list("", "Python is fun") == ['Python', 'is', 'fun']
  assert string_to_list("Hello world", "") == ['Hello', 'world']
  assert string_to_list("", "") == []
output: def string_to_list(str1, str2):
      if not str1:
          return str2.split()
      if not str2:
          return str1.split()
      return str1.split() + str2.split()