title: redux form, Field component issues
body: <p>I have some issues using "Field" component in Redux Form in my code. Just follow the simple example on redux-form website.</p>
  
  <pre><code>/* MyForm.jsx */
  ...
  import { Field, reduxForm } from 'redux-form';
  
  class MyForm extends Component {
      ...
      &lt;form onSubmit={handleSubmit(...)}&gt;
          &lt;div&gt;
              &lt;label&gt;First Name&lt;/label&gt;
              &lt;div&gt;
                  &lt;Field name="firstName" component="input" type="text" placeholder="First Name"/&gt;
              &lt;/div&gt;
          &lt;/div&gt;
          ...
  }
  
  export default reduxForm({
      form: 'myForm'
  })(MyForm);
  </code></pre>
  
  <p>Here is the parent component that use the redux form.</p>
  
  <pre><code>/* page.jsx */
  import MyForm from './MyForm';
  ...
  &lt;MyForm/&gt;
  ...
  </code></pre>
  
  <p>The form does not render and in console the error says:</p>
  
  <p><em><code>React.createElement: type should not be null, undefined, boolean, or number. It should be a string (for DOM elements) or a ReactClass (for composite components).</code></em></p>
  
  <p><em><code>Uncaught Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined.</code></em> </p>
  
  <p>However, if I use material-ui or bootstrap form field, it works fine. </p>
  
  <p>I mounted the form reducer before render the form:</p>
  
  <pre><code>import {reducer as formReducer} from 'redux-form';
  const myReducer = combineReducers({
      ...
      form: formReducer
  });
  </code></pre>
  
  <p>Any ideas why Fields component does not work?</p>
  
  <p>Thanks,</p>