input: Write a function to find the maximum element in the given array. If the array is empty, return None.
  assert get_max_element([1, 10, 50, 3, 8])==50
  assert get_max_element([-3, -10, -1, -5])==-1
  assert get_max_element([100])==100
  assert get_max_element([])==None
output: def get_max_element(arr):
      if not arr:
          return None
      return max(arr)