title: TypeError: Cannot read property 'string' of undefined ; install library boron
body: <p>I installed the <a href="https://github.com/yuanyan/boron" rel="nofollow noreferrer">https://github.com/yuanyan/boron</a> library, but I have error:</p>
  
  <blockquote>
    <p>TypeError: Cannot read property 'string' of undefined</p>
    
    <p>TypeError: Cannot read property 'string' of undefined
    push../node_modules/boron/modalFactory.js.module.exports
    C:/Users/m/Desktop/chrome-extension/node_modules/boron/modalFactory.js:10
    7 | module.exports = function (animation) {    8 |   return
    React.createClass({    9 |     propTypes: {</p>
    
    <blockquote>
      <p>10 |       className: React.PropTypes.string,   11 |       // Close the modal when esc is pressed? Defaults to true.   12 |<br>
      keyboard: React.PropTypes.bool,   13 |       onShow:
      React.PropTypes.func,</p>
    </blockquote>
  </blockquote>