I am developing a webapp in MERN stack, while doing so I encountered with an error , please help. When I try to update the user it gives me an error, Callback must be a function, got '[object Object]'.

This is the API.

It is guaranteed that user always exists.

module.exports.addBlog=(req,res)=>{
    const {title,data} = req.body.blog;
    console.log(title,data);
    const {email} = req.body;
    const newblog ={
        title,
        data
    }
    userSchema.findOneAndUpdate(
        {email},
        {$push:{blogArray:newblog}},
        {upsert:true},
        {useFindAndModify:false}
        )
        .then(res=>console.log(res))
        .catch(err=>console.log(err));
   
    return res.json({msg:"Blog added successfully"});
}

This is the userschema.

const userSchema = new mongoose.Schema({
    firstname:{
        type:String,
        required:true,
        lowercase:true
    },
    lastname:{
        type:String,
        required:true,
        lowercase:true
    },
    email:{
        type:String,
        required:true,
        lowercase:true
    },
    password:{
        type:String,
        required:true
    },
   blogArray:[
       {
        title:{
            type:String,
             required:true
        },
        data:{
            type:String,
            required:true
        }
    }
   ]
});