input: Write a function to find the maximum element in an array of numbers. If the array is empty, return None. The function should return the maximum number found in the array.
  
  assert find_max_element([1, 43, 78, 3, 92, 42]) == 92
  assert find_max_element([0, -5, 10, 15, -1]) == 15
  assert find_max_element([]) == None
  assert find_max_element([3]) == 3
  assert find_max_element([-10, -20, -5, -15]) == -5
  
output: def find_max_element(arr):
      if not arr:
          return None
      return max(arr)