input: Write a function to find the maximum element in an array of numbers. If the array is empty, return None.
  def find_max_element(numbers):
      if not numbers:
          return None
      return max(numbers)
  
  assert find_max_element([1, 43, 78, 3, 92, 42])==92
  assert find_max_element([])==None
  assert find_max_element([10, 20, 30, 40])==40
  assert find_max_element([5])==5
output: def find_max_element(numbers):
      if not numbers:
          return None
      return max(numbers)