jsp的Integer.parseInt(request.getParameter(““))；语句报错：Cannot parse null string

@WebServlet("/insertSer")
public class insertSer extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        this.doPost(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        String id=request.getParameter("id");
        String name=request.getParameter("name");
        String author=request.getParameter("author");
        String tid=request.getParameter("tid");
        int tid1=Integer.parseInt(tid);
        DaoFromDB db=new DaoFromDB();
        boolean mark=db.insert(id, name, author,tid1);
        if(mark==true){
            int currentPauthor=Integer.parseInt(request.getParameter("currentPauthor"));  //报错语句

            request.getSession().setAttribute("currentPauthor", currentPauthor);
            ArrayList<book> books=db.display(currentPauthor);
            request.setAttribute("books", books);
            request.getRequestDispatcher("/jsp/display.jsp").forward(request, response);
        }
    }

}

有大佬知道怎么解决嘛？