input: Write a function to print out the largest value from a given list of numbers.
  assert get_max_value([2, 4, 1, 6])==6
  assert get_max_value([10, 5, 9, 3])==10
  assert get_max_value([1, 1, 1, 1])==1
  assert get_max_value([7])==7
  assert get_max_value([])==None
output: def get_max_value(numbers):
      if not numbers:
          return None
      return max(numbers)