input: 
  def get_max_value(numbers):
      """ Find and return the largest value from a given list of numbers.
      >>> get_max_value([2, 4, 1, 6])
      6
      >>> get_max_value([10, 5, 8, 22, 15])
      22
      """
      return max(numbers)
  
output:     if not numbers:
          return None