input: Write a function to find the maximum element in a given array. The function should return the maximum element in the array. If the array is empty, the function should return None.
  assert find_max_element([1, 10, 50, 3, 8])==50
  assert find_max_element([15, -1, 0, 45, 12])==45
  assert find_max_element([-3, -5, -1, -8])==-1
  assert find_max_element([])==None
  assert find_max_element([7])==7
output: def find_max_element(arr):
      if not arr:
          return None
      return max(arr)