Comment 1 for bug 449372

The function in question is:
static int __pyx_tp_traverse_21_dirstate_helpers_pyx_Reader(PyObject *o, visitproc v, void *a) {
  int e;
  struct __pyx_obj_21_dirstate_helpers_pyx_Reader *p = (struct __pyx_obj_21_dirstate_helpers_pyx_Reader *)o;
  if (p->state) {
    e = (*v)(p->state, a); if (e) return e;
  }
  if (p->text) {
    e = (*v)(p->text, a); if (e) return e; // line 8401
  }
  return 0;
}

Since p-> have already been used I guess it has to be v that is NULL.