title: Redux: props are undefined when rendering
body: <p>trying to implement ReactRedux with my own example, I'm a bit struggling. It appears as if my props aren't given any value and are still undefined when React renders them. Is my approach in general correct and only a simple error or is there something really wrong?</p>
  
  <p>I've recreated my problem in <a href="http://jsbin.com/xupuhozixa/edit?js,output" rel="nofollow">jsbin</a>:</p>
  
  <pre><code>class Walls extends React.Component {
      render() {
      return (
          &lt;div id="main"&gt;
              &lt;div&gt;volume: {this.props.volume}m³&lt;/div&gt;
          &lt;/div&gt;
      )}
  }
  
  const mapStateToProps = (state) =&gt; {
      return {
          volume: state.volume
      };
  }
  
  const WallContainer = connect(mapStateToProps)(Walls);
  
  function reducer(state = Map(), action) {
    switch (action.type) {
    case 'SET_STATE':
      return state.merge(action.state);
    }
    return state;
  } 
  
  const store = createStore(reducer)
  store.dispatch({
      type: 'SET_STATE',
      state: {"volume":1567.571734691151}
  })
  
  ReactDOM.render(
          &lt;Provider store={store}&gt;
              &lt;WallContainer /&gt;
          &lt;/Provider&gt;, 
          document.getElementById('root')
  );
  </code></pre>