input: Write a function to get the maximum and minimum values in a given list.
  assert get_max_min([3, 4, 5, 1, 2])==(1, 5)
  assert get_max_min([10, 20, 30, 40, 50])==(10, 50)
  assert get_max_min([-1, -5, -10, -2])==(-10, -1)
  assert get_max_min([0])==(0, 0)
  assert get_max_min([])==(None, None)
output: def get_max_min(lst):
      if not lst:
          return None, None
      return min(lst), max(lst)