I am trying to create a doc to model with mongoose but model.create() does not return any promise

it seems that the create method does not return any promise that then can handle
I tried different things but nothing worked
this is my routes file

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

const express = require("express")
const router = express.Router();


const controller = require("./controller")

router.post("/signup", controller.create);
 

module.exports = router;

<!-- end snippet -->

and this is my model file

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

const mongoose = require('mongoose');

const User = new mongoose.Schema(
  {
    firstName: {
      type: String,
      required: true
    },
    lastName: {
      type: String,
      required: true
    },
    
    picture: {
      type: String
    },
    password: {
      type: String,
      select: false
    },
    email: {
      required: true,
      type: String,
      unique: true
    }
  },
  {
    timestamps: true
  }
);

User.index({
  firstName: 'text',
  lastName: 'text',
});

module.exports = mongoose.model('User', User);

<!-- end snippet -->

and this is the controller file

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

const User = require('./model');
const { hash, compareHash } = require('../lib/util');
const { createToken, findUserByToken } = require('../lib/auth');

const cookieIsSecure = process.env.ENVIRONMENT === 'production';

exports.create = async (req, res) => {
  const password = await hash(req.body.password);
  const rawUser = {
    ...req.body,
    password,
  };
  
  User.create(rawUser)
    .then(async user => {
       return user.save();
    })
    .then(async user => {
      const newUser = user.toObject();
      res.send(newUser);
    })
    .catch(err => {
      if (err.code === 11000) {
        res.status(400).send({ message: 'A user with this email address has already registered.' });
        return;
      }
      res.status(500).send({ message: 'An unexpected error occurred' });
    });
};

<!-- end snippet -->

it always return the 500 error "an unexpected error occurred"
which is not really specific. and i do not know what is the problem exactly. but I am sure it has something to do with the model.create() it does not return any promise.

Here you are mixing methods. create doesn't want save in it as it's implicit:

https://mongoosejs.com/docs/api.html#model_Model.create

Please try this, I've refactored your code a bit and added much easier to read and use try/catch:

const rawUser = new User({ ...req.body, password});

try {
  await rawUser.save();
  res.status(201).send(newUser);
} catch(err) {
  if (err.code === 11000) return res.status(400).send({ message: 'A user with this email address has already registered.' });
  res.status(500).send({ message: 'An unexpected error occurred' });  
}

You need to use async/await like this:

exports.create = async (req, res) => {
  try {
    const password = await hash(req.body.password);
    const rawUser = {
      ...req.body,
      password
    };

    const user = await User.create(rawUser);
    const newUser = user.toObject();
    res.send(newUser);
  } catch (err) {
    console.log("ERROR: ", err);
    if (err.code === 11000) {
      return res.status(400).send({
        message: "A user with this email address has already registered."
      });
    }
    res.status(500).send({ message: "An unexpected error occurred" });
  }
};