input: Write a function to convert a given string to a list of integers. The given string consists of integers separated by commas. The function should return a list of integers when the string is passed to it.
  assert to_int_list("1,2,3,4,5")==[1, 2, 3, 4, 5]
  assert to_int_list("10,20,30")==[10, 20, 30]
  assert to_int_list("0,0,0")==[0, 0, 0]
  assert to_int_list("-1,1,-9")==[-1, 1, -9]
  assert to_int_list("")==[]
output: def to_int_list(s):
      return [int(x) for x in s.split(',') if x]