TypeError: Cannot read property 'string' of undefined

[zikwall]

/node_modules/react-hammerjs/src/Hammer.js:100

  97 | var HammerComponent = React.createClass({
   98 |   displayName: 'Hammer',
   99 |   propTypes: {
> 100 |     className: React.PropTypes.string
  101 |   },
  102 |   componentDidMount: function () {
  103 |     this.hammer = new Hammer(ReactDOM.findDOMNode(this));

I did everything according to the documentation, even tried just copying your code, but it still doesn’t work