React Data Grid fails at src/DataGrid.tsx:268 throwing a : TypeError: rows is undefined

I am using the example code provided on the React Data Grid website at https://adazzle.github.io/react-data-grid/docs/examples/simple-grid without any changes :

import React from "react";
import ReactDOM from "react-dom";
import ReactDataGrid from "react-data-grid";
import "./styles.css";

const columns = [
 { key: "id", name: "ID", editable: true },
 { key: "title", name: "Title", editable: true },
 { key: "complete", name: "Complete", editable: true }
];

const rows = [
 { id: 0, title: "Task 1", complete: 20 },
 { id: 1, title: "Task 2", complete: 40 },
 { id: 2, title: "Task 3", complete: 60 }
];

class Example extends React.Component {
 state = { rows };

onGridRowsUpdated = ({ fromRow, toRow, updated }) => {
this.setState(state => {
  const rows = state.rows.slice();
  for (let i = fromRow; i <= toRow; i++) {
    rows[i] = { ...rows[i], ...updated };
  }
  return { rows };
 });
 };
render() {
 return (
  <ReactDataGrid
    columns={columns}
    rowGetter={i => this.state.rows[i]}
    rowsCount={3}
    onGridRowsUpdated={this.onGridRowsUpdated}
    enableCellSelect={true}
  />
);
}
}

const rootElement = document.getElementById("root");
ReactDOM.render(<Example />, rootElement);

but got a type error back from React Data Grid. What I am doing wrongly ?