input: Write a function to combine the words from two input strings into a single list. If the given strings are empty, return an empty list.
  def string_to_list(s1, s2):
      if not s1 and not s2:
          return []
      s1_list = s1.split()
      s2_list = s2.split()
      output_list = s1_list + s2_list
      return output_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("", "")==[]
  assert string_to_list("Hello World", "")==["Hello", "World"]
  assert string_to_list("", "Testing is fun")==["Testing", "is", "fun"]
output: def string_to_list(s1, s2):
      if not s1 and not s2:
          return []
      s1_list = s1.split()
      s2_list = s2.split()
      output_list = s1_list + s2_list
      return output_list