title: Element type is invalid (got: undefined) for react-redux component
body: <p>I'm trying to create a component for <code>redux-form</code>. Here is my component</p>
  
  <pre><code>import React, { PropTypes } from 'react'
  import Input from 'react-toolbox'
  
  export const TextField = ({ input, meta: { touched, error }, ...custom }) =&gt; (
    &lt;Input
      error={touched &amp;&amp; error}
      {...input}
      {...custom}
    /&gt;
  )
  
  TextField.propTypes = {
    input: PropTypes.object,
    meta: PropTypes.object
  }
  
  export default TextField
  </code></pre>
  
  <p>I also create an <code>index.js</code> file to easily import it </p>
  
  <pre><code>import TextField from './TextField'   
  export default TextField
  </code></pre>
  
  <p>Then I use it like this </p>
  
  <pre><code>import TextField from 'components/TextField'
  import { Field } from 'redux-form'
  &lt;form onSubmit={props.handleSubmit(props.loginUser)}&gt;
    &lt;Field type='email' label='Email' name='email' component={TextField} required /&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>But I get this error </p>
  
  <blockquote>
    <p>Error: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. Check the render method of <code>TextField</code>.</p>
  </blockquote>
  
  <p>I check again an again</p>
  
  <ul>
  <li><a href="http://redux-form.com/6.0.0-alpha.4/docs/api/Field.md/" rel="nofollow noreferrer">the redux form doc</a></li>
  <li>other related topic on SO like this <a href="https://stackoverflow.com/questions/34130539/uncaught-error-invariant-violation-element-type-is-invalid-expected-a-string">one</a> or this <a href="https://stackoverflow.com/questions/34135827/uncaught-typeerror-cannot-read-property-createroutefromreactelement-of-undefi">one</a></li>
  </ul>