issue with setting hardhat config.

[sandeepV2]

Facing an error when running hardhat clean. The error is asking for string type and url provided is string !.

Error HH8: There's one or more errors in your config file:

• Invalid value undefined for HardhatConfig.networks.polygon_mumbai.url - Expected a value of type string.

To learn more about Hardhat's configuration, please go to https://hardhat.org/config/

Contents of hardhat.config.js file.

require("@nomiclabs/hardhat-waffle");
require("@nomiclabs/hardhat-etherscan");

const dotenv = require("dotenv");
dotenv.config();

/** @type import('hardhat/config').HardhatUserConfig */
module.exports = {
  solidity: "0.8.9",
  defaultNetwork: "polygon_mumbai",
  networks: {
    polygon_mumbai: {
      uri: "https://rpc-mumbai.maticvigil.com/",
      accounts: [process.env.PRIVATE_KEY],
    },
  },
  etherscan: {
    apiKey: process.env.POLYGON_API_KEY,
  },
};