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