NullPointerException错误，无法解决

Question

获取NullPointerException并搜索所有可能的方法，但无法找到我收到此错误的原因。这是我的代码; 该错误在controllerServletSign.java行中：36 if（（sign.search（m））== true）

daoSign.java

public class daoSign {
Connection connection = null;
public daoSign(){
    connection = Utility.getConnection();
}
public boolean search(modelLogin m){

    try {
        String name = m.getName();
        String password = m.getPassword();
         Statement stmt = connection.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT * FROM user");
         while (rs.next()) {
         if((rs.getString("name")== name) && (rs.getString("password")==    password)){
                 return true;
             }
         }
    } catch (SQLException e) {
        e.printStackTrace();
    }
     return false;
    }

  }

controllerServletSign.java

@WebServlet("/controllerServletSign")
public class controllerServletSign extends HttpServlet {
private static final long serialVersionUID = 1L;
daoSign sign;
modelLogin m = new modelLogin();
protected void doGet(HttpServletRequest request, HttpServletResponse          response) throws ServletException, IOException {

}

/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 */
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html");
    String name = request.getParameter("name");
    String password = request.getParameter("passsword");

    m.setName(name);
    m.setPassword(password);

    if((sign.search(m))== true){    //this line is giving exception
        System.out.println("welcome " + name);
    }
    else{
        System.out.println("worng");
    }

}