报这个错是为啥Exception in thread "main" java.lang.NullPointerException at com.spring.dao.Goddess_dao.query(Goddess_dao.java:28) at com.spring.action.GoddessAction.main(GoddessAction.java:10)

package com.spring.action;

import java.util.List;

import com.spring.dao.*;

import com.spring.model.Goddess;

public class GoddessAction {

public static void main(String[] args) throws Exception {

Goddess_dao g = new Goddess_dao();

List<Goddess> gs = g.query();

for (Goddess goddess : gs) {

System.out.println(goddess.getUser_name()+","+goddess.getAge());

}

}

}