input: Write a function to sort a given array in ascending order using the bubble sort algorithm. The function should modify the input array in-place. If the given array is empty, it should return immediately without any changes.
  
  def bubble_sort(arr): 
      if not arr:
          return
      n = len(arr) 
      for i in range(n-1):
          for j in range(0, n-i-1): 
              if arr[j] > arr[j+1] : 
                  arr[j], arr[j+1] = arr[j+1], arr[j] 
  
  arr = [3,7,4,1]
  bubble_sort(arr) 
  assert arr == [1, 3, 4, 7]
  
  arr = []
  bubble_sort(arr) 
  assert arr == []
output: def bubble_sort(arr): 
      if not arr:
          return
      n = len(arr) 
      for i in range(n-1):
          for j in range(0, n-i-1): 
              if arr[j] > arr[j+1] : 
                  arr[j], arr[j+1] = arr[j+1], arr[j]