React component classes must extend React.Component

[teone]

Just installed this package and trying to display some datas I'm getting this errors:

Warning: PieChart(...): React component classes must extend React.Component.warning 
Uncaught Invariant Violation: PieChart.render(): A valid ReactComponent must be returned. You may have returned undefined, an array or some other invalid object.

What can this be about?

I would also suggest to display sample data format in the readme.