SyntaxError: Unexpected token - in JSON at position 0

Question

I am following online tutorial on youtube which is about building social network using react as front end and firebase functions as back end and I keep getting this error using the uploadImage route and I have no idea where the problem is, if someone could explain why I am having this error.

exports.uploadImage=(req,res)=>{
    const BusBoy=require('busboy')
    const path=require('path')
    const os=require('os')
    const fs =require('fs')

    let imageFileName;
    let imageToBeUploaded={}

    const busboy = new BusBoy({ headers: req.headers })

    busboy.on('file',(fieldname, file, filename, encoding, mimetype)=>{
        // image.png
        const imageExtension = filename.split('.')[filename.split('.').length - 1]
         imageFileName = `${Math.round(Math.random()*100000000000)}.${imageExtension}`;
        const filepath = path.join(os.tmpdir(),imageFileName);
        imageToBeUploaded={filepath, mimetype};
        file.pipe(fs.createWriteStream(filepath))
    });
    busboy.on('finish',()=>{
        admin
        .storage()
        .bucket()
        .upload(imageToBeUploaded.filepath,{
            resumable:false,
            metadata:{
                metadata:{
                    contentType: imageToBeUploaded.mimetype
                }
            }
        })
        .then(()=>{
            const imageUrl = `https://firebasestorage.googleapis.com/v0/b/${config.storageBucket}/o/${imageFileName}?alt=media`
            return db.doc(`/users/${req.user.handle}`).update({imageUrl})
        })
        .then(()=>{
            return res.json({message:'Image uploaded Successfully'})
        })
        .catch(err=>{
            console.error(err);
            return res.status(500).json({error:err.code})
        })
    })
    busboy.end(req.rawBody)
}