input: Write a function to find the maximum element in the given array of numbers. If the array is empty, return None.
  assert find_max_element([1, 43, 78, 3, 92, 42])==92
  assert find_max_element([1, 2, 3, 4, 5])==5
  assert find_max_element([99, 100, 12, 88])==100
  assert find_max_element([-1, -5, -3, 0])==0
  assert find_max_element([])==None
output: def find_max_element(arr):
      if not arr:
          return None
      return max(arr)