Filter gives NullPointerException

Question

Here's my servlet code:

@WebServlet("/Admin")
public class Admin extends HttpServlet {

// some code goes here

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    OrdersQuery query = new OrdersQuery();

    if (request.getParameter("deleteOrderBtn") != null) {
        deleteOrderById(Integer.valueOf(request.getParameter("deleteOrderBtn")));
    }else {
        Object allOrders = query.getAllOrders();
        request.setAttribute("allOrders", allOrders);

        RequestDispatcher rd = request.getRequestDispatcher("admin.jsp");
        rd.forward(request, response);
    }
}

}

And my authentication filter:

    @WebFilter("/Admin")
    public class AdminFilter implements Filter {
    public void doFilter(ServletRequest request, ServletResponse response,          FilterChain chain) throws IOException, ServletException {

    String login = request.getParameter("adminLogin");
    String password = request.getParameter("adminPassword");
    if (login.equals(LOGIN) && password.equals(PASSWORD)) {
        chain.doFilter(request, response);
    }else {
        RequestDispatcher rd = request.getRequestDispatcher("error.jsp");
        rd.forward(request, response);
    }

}

So when I am pressing the deleteOrderBtn button it gives me NullPointerException and refers to the Filter and this line from it:

if (login.equals(LOGIN) && password.equals(PASSWORD)) {

But I have no idea why. So can you please look at my problem?