input: Write a function to convert a given string to a list of integers. The string contains integers separated by commas. If the input string is empty, return an empty list.
  
  def to_int_list(s):
      return [int(x) for x in s.split(',')] if s else []
  
  assert to_int_list("1,2,3,4,5")==[1, 2, 3, 4, 5]
  assert to_int_list("10,-20,30,40,50")==[10, -20, 30, 40, 50]
  assert to_int_list("")==[]
  assert to_int_list("1,2,3,4,5,6,7,8,9")==[1, 2, 3, 4, 5, 6, 7, 8, 9]
  assert to_int_list("100,200,300,400")==[100, 200, 300, 400]
output: 
  def to_int_list(s):
      return [int(x) for x in s.split(',')] if s else []
  