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([-5, -2, -10, -1])==-1
  assert find_max_element([34])==34
  assert find_max_element([])==None
  assert find_max_element([99, 99, 99, 99])==99
output: def find_max_element(arr):
      if not arr:
          return None
      max_element = arr[0]
      for num in arr:
          if num > max_element:
              max_element = num
      return max_element