if (tid == null | tid.getReference().get () == null)
if (tid.getReference().get () == null)
  public StepFilter (ThreadId tid, int size, int depth)    throws InvalidThreadException  {    if (tid == null | tid.getReference().get () == null)      throw new InvalidThreadException (tid.getId ());    _tid = tid;    _size = size;    _depth = depth;  }