UnhandledPromiseRejectionWarning: MongooseServerSelectionError Bug?*

What is the current behavior?

• hello there I am trying to connect mongoose with URL string included everything is fine but after console.log("mongoDB database connection established successfully") this is not showing this console's text but an error is coming there

const express = require("express");
const cors = require("cors");
const mongoose = require("mongoose");
require("dotenv").config();
const app = express();
const port = process.env.PORT || 5000;

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

const uri = process.env.ATLAS_URI;
// mongoose.connect(uri,{useNewUrlParser:true,useCreateIndex:true,useUnifiedTopology:true} 
   // ); // update the code provided below

mongoose
     .connect( uri, { useNewUrlParser: true, useCreateIndex: true, useUnifiedTopology: true })
     .then(() => console.log( 'Database Connected' ))
     .catch(err => console.log( err ));

app.listen(port, () => {
  console.log(`server is running on port ${port}`);
});

server.js file code above and in .env the URI key is given

What is the expected behavior?

• the expected output is MongoDB database connection established successfully.

What are the versions of Node.js, Mongoose, and MongoDB you are using? Note that "latest" is not a version.

• "cors": "^2.8.5", "dotenv": "^8.2.0", "express": "^4.17.1", "mongoose": "^5.11.14",