input: Write a function to find the maximum element in an array of numbers. The function should take one parameter, a list of numbers, and return the maximum number in the list. If the array is empty, the function should return None.
  assert find_max_element([1, 43, 78, 3, 92, 42])==92
  assert find_max_element([3, 4, 5, 1, 2])==5
  assert find_max_element([-1, -43, -78, -3, -92, -42])==-1
  assert find_max_element([])==None
output: def find_max_element(arr):
      if not arr:
          return None
      return max(arr)