I was trying to upload images to mongodb database. And Then got this error which I am not able to resolve. Can someone help!

The code after all the require statements is show below

// MONGOOSE CONNECTION
const conn = mongoose.createConnection(mongoURI);
// GRID FS
let gfs;
conn.once('open' , ()=>{
   // init stream
   gfs = Grid(conn.db , mongoose.mongo);
   gfs.collection('uploads');
});
// MULTER
const storage = new GridFsStorage({
    url: mongoURI,
    file: (req, file) => {
      return new Promise((resolve, reject) => {
      crypto.randomBytes(16, (err, buf) => {
      if (err) {
        return reject(err);
      }
      const filename = buf.toString('hex') + path.extname(file.originalname);
      const fileInfo = {
        filename: filename,
        bucketName: 'uploads'
      };
      resolve(fileInfo);
    });
  });
}
});

const upload = multer({storage}).single('file');

Then When i tried to show the file object saved in the database using gfs.file.find(), it worked

app.get("/files/:filename" , (req , res)=>{
gfs.files.findOne({filename : req.params.filename} , (err , file)=>{
    if(!file){
        return res.json({err : "No file exists"});
    }
    return res.json(file)
})
});

The above code worked and showed the json object when called. But when tried to show the image not as json but as the actual image using createReadStream , It broke

app.get("/image/:filename" , (req , res)=>{
gfs.files.findOne({filename : req.params.filename} , (err , file)=>{
    if(!file){
        return res.json({err : "No file exists"});
    }
    // file exists
    // if it is an image
    if(file.contentType === 'image/jpeg' || file.contentType === 'image/png'){
        // Read output to browser
        const readstream = gfs.createReadStream(file.filename);
        readstream.pipe(res);
    }
    else{
        res.status(404).json({err : "not an image"});
    }
});
});