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([]) == None
  assert find_max_element([4, 2, 9, 7]) == 9
  assert find_max_element([1]) == 1
  assert find_max_element([-5, -2, -10, -3]) == -2
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