input: Write a python function to find the maximum value in a list.
  assert get_max([1, 2, 3, 4, 5]) == 5
  assert get_max([10, 4, 2, 8, 6]) == 10
  assert get_max([-1, -4, -3, -2, -5]) == -1
output: def get_max(lst):
      if not lst:
          return None
      max_value = lst[0]
      for num in lst:
          if num > max_value:
              max_value = num
      return max_value