input: Write a function to convert a given string to a list of integers.
  
  def to_int_list(s):
      return [int(x) for x in s.split(',')]
  
  assert to_int_list("1,2,3,4,5")==[1, 2, 3, 4, 5]
  assert to_int_list("10,20,30,40")==[10, 20, 30, 40]
  assert to_int_list("0,0,0,0")==[0, 0, 0, 0]
  assert to_int_list("-1,-2,-3,-4")==[-1, -2, -3, -4]
  assert to_int_list("")==[]
output: def to_int_list(s):
      return [int(x) for x in s.split(',') if x]