node.js - mongoose 查询数据库 回调报错为null？求帮助啊

//dbconf

var mongo = require('mongo'); //引入mysql模块
var mongoose = require('mongoose'); //引入mongoose模块
var shortid = require('shortid');
var db = mongoose.connect('mongodb://127.0.0.1/FBMS')
var Schema = mongoose.Schema;
db.connection.on('error',function(error){

console.log(error);

})
db.connection.on('open',function(){

console.log('open mongoDB');

})
var accountSchema= new Schema({

_id: {
    type: String,
    unique: true,
    'default': shortid.generate
},
username:{type:String ,index:{unique:true}},
password:String,
avataimgurl:{type:String,default:''},
cellphone:Number,
address:String,
device:{stuff:String},
remarks:String

})

module.exports= mongoose.model('account',accountSchema); //连接对象导出

//account

var dbconf = require('./dbconf'); //导入dbconf模块
var data={code:'200',msg:'',username:''};
var checkAccount={

check:function(_req,_res){
    dbconf.find({'username':'wangpeng'},function(err,results,fields){
        if(err){
                console.log("数据库报错："+err);
                console.log("："+results);
                console.log("："+fields);
        
        }
        });
}

}

module.exports = checkAccount;