Trace 0:
  Transitions:
  error: NullPtrArgument()
  error: calling PyString_ConcatAndDel with NULL as argument 1 (0B) at tests/cpychecker/refcounts/PyString_ConcatAndDel/null-lhs/input.c:28
  Exception:
    (struct PyObject *)0 from tests/cpychecker/refcounts/PyString_ConcatAndDel/null-lhs/input.c:27