input: Write a function to combine two strings and reverse the result in Python. If either of the strings is empty, return an empty string.
  
  assert combine_and_reverse("Hello ", "world!")=="!dlrow olleH"
  assert combine_and_reverse("Python", " Rocks!")=="!skcoR nohtyP"
  assert combine_and_reverse("", "No Input")==""
  assert combine_and_reverse("Empty Second", "")==""
  assert combine_and_reverse("", "")==""
output: def combine_and_reverse(s1, s2):
      if s1 == "" or s2 == "":
          return ""
      combined = s1 + s2
      return combined[::-1]