private static InvocationExprent isAssertionError(Statement stat) {

    if (stat == null || stat.getExprents() == null || stat.getExprents().size() != 1) {
      return null;
    }

    Exprent expr = stat.getExprents().get(0);

    if (expr.type == Exprent.EXPRENT_EXIT) {
      ExitExprent exexpr = (ExitExprent)expr;
      if (exexpr.getExitType() == ExitExprent.EXIT_THROW && exexpr.getValue().type == Exprent.EXPRENT_NEW) {
        NewExprent nexpr = (NewExprent)exexpr.getValue();
        if (CLASS_ASSERTION_ERROR.equals(nexpr.getNewType()) && nexpr.getConstructor() != null) {
          return nexpr.getConstructor();
        }
      }
    }

    return null;
  }
private static InvocationExprent isAssertionError(Statement stat)