== test ==
fun test(s: IntProgression?) {
    s?.first
}
---------------------
L0:
  1 <START>
    v(s: IntProgression?)
    magic[FAKE_INITIALIZER](s: IntProgression?) -> <v0>
    w(s|<v0>)
  2 mark({ s?.first })
    mark(s?.first)
    jf(L2)                                                 NEXT:[<END>, r(s) -> <v1>]
    r(s) -> <v1>
    r(first|<v1>) -> <v2>
L1:
L2 [result of call]:
  1 <END>                                                  NEXT:[<SINK>]                                                 PREV:[jf(L2), r(first|<v1>) -> <v2>]
error:
    <ERROR>                                                PREV:[]
sink:
    <SINK>                                                 PREV:[<ERROR>, <END>]
=====================