input: Write a function to find the maximum element in the given array. If the array is empty, return None.
  
  assert find_max_element([1, 10, 50, 3, 8]) == 50
  assert find_max_element([1, 2, 3, 4, 5]) == 5
  assert find_max_element([-1, -2, -3, -4, -5]) == -1
  assert find_max_element([]) == None
output: def find_max_element(arr):
      if not arr:
          return None
      return max(arr)