input: Write a function to swap the values of two variables. The function should take two parameters, swap them, and return the swapped values. If either of the variables is None, return the original values.
  assert swap_values(5, 10) == (10, 5)
  assert swap_values(10, None) == (10, None)
  assert swap_values(None, 5) == (None, 5)
  assert swap_values(None, None) == (None, None)
  assert swap_values(0, 0) == (0, 0)
output: def swap_values(a, b):
      if a is None or b is None:
          return a, b
      return b, a