发出post请求时出现意外字段错误?

我在发出post请求时遇到意外的字段错误?这是我的node js代码

var express = require('express');
var multer = require('multer');
var bodyParser = require('body-parser');
var cors = require('cors');
var app = express();
var PORT = process.env.PORT || 3000;
var upload = multer({ dest: 'uploads/' })


// use of body parser
app.use(bodyParser.urlencoded({
    extended: true
}));

app.use(bodyParser.json());
app.use(cors());




app.post('/upload',upload.single('avatar'), function (req, res,next) {
console.log(req.file);
console.log('hello');
res.send({data:'sss'})
});


app.listen(PORT, () => {
    console.log(`App is listening to ${PORT}`);
})

我用这个插件上传文件 https://www.npmjs.com/package/multer 当我完成任务时 postman

**App is listening to 3000
Error: Unexpected field
    at makeError (C:\Users\B0207296\WebstormProjects\uploadFile\node_modules\multer\lib\make-error.js:12:13)
    at wrappedFileFilter (C:\Users\B0207296\WebstormProjects\uploadFile\node_modules\multer\index.js:40:19)
    at Busboy.<anonymous> (C:\Users\B0207296\WebstormProjects\uploadFile\node_modules\multer\lib\make-middleware.js:114:7)
    at emitMany (events.js:147:13)
    at Busboy.emit (events.js:224:7)
    at Busboy.emit (C:\Users\B0207296\WebstormProjects\uploadFile\node_modules\busboy\lib\main.js:38:33)
    at PartStream.<anonymous> (C:\Users\B0207296\WebstormProjects\uploadFile\node_modules\busboy\lib\types\multipart.js:213:13)
    at emitOne (events.js:116:13)
    at PartStream.emit (events.js:211:7)
    at HeaderParser.<anonymous> (C:\Users\B0207296\WebstormProjects\uploadFile\node_modules\dicer\lib\Dicer.js:51:16)**

邮递员图像