Error with Truffle React (the contract doesn't have address)

Question

Someone knows something about this error with Truffle React box? Must be my Metamask wallet address but it is already in my truffle-config file.

I leave the App.js file here (I didn't make it. It's just the code of Truffle React Box). I've just followed the steps here: https://www.trufflesuite.com/boxes/react

import React, { Component } from "react";
import SimpleStorageContract from "./contracts/SimpleStorage.json";
import getWeb3 from "./getWeb3";

import "./App.css";

class App extends Component {
  state = { storageValue: 0, web3: null, accounts: null, contract: null };

  componentDidMount = async () => {
    try {
      // Get network provider and web3 instance.
      const web3 = await getWeb3();
      // Use web3 to get the user's accounts.
      const accounts = await web3.eth.getAccounts();

      // Get the contract instance.
      const networkId = await web3.eth.net.getId();
      const deployedNetwork = SimpleStorageContract.networks[networkId];
      const instance = new web3.eth.Contract(
        SimpleStorageContract.abi,
        deployedNetwork && deployedNetwork.address,
      );


      // Set web3, accounts, and contract to the state, and then proceed with an
      // example of interacting with the contract's methods.
      this.setState({ web3, accounts, contract: instance }, this.runExample);
    } catch (error) {
      // Catch any errors for any of the above operations.
      alert(
        `Failed to load web3, accounts, or contract. Check console for details.`,
      );
      console.error(error);
    }
  };

  runExample = async () => {
    const { accounts, contract } = this.state;

    // Stores a given value, 5 by default.
    await contract.methods.set(5).send({ from: accounts[0] });

    // Get the value from the contract to prove it worked.
    const response = await contract.methods.get().call();

    // Update state with the result.
    this.setState({ storageValue: response });
  };

  render() {
    if (!this.state.web3) {
      return <div>Loading Web3, accounts, and contract...</div>;
    }
    return (
      <div className="App">
        <h1>Good to Go!</h1>
        <p>Your Truffle Box is installed and ready.</p>
        <h2>Smart Contract Example</h2>
        <p>
          If your contracts compiled and migrated successfully, below will show
          a stored value of 5 (by default).
        </p>
        <p>
          Try changing the value stored on <strong>line 42</strong> of App.js.
        </p>
        <div>The stored value is: {this.state.storageValue}</div>
      </div>
    );
  }
}

export default App;

SOLUTION:

After this piece of code:

      const instance = new web3.eth.Contract(
        SimpleStorageContract.abi,
        deployedNetwork && deployedNetwork.address,
      );

I've added this line:

instance.options.address = "[my contract' address on kovan]"