title: React Redux - Field onChange returning undefined
body: <p>In my component, I have a redux <code>Field</code> where all I'm trying to do is all a function when the field gets updated via Datepicker, however when I do that, </p>
  
  <pre><code>render() {
    return (
         &lt;Field onChange={this.updateStartDate} name='startDate' component={DatePicker} hintText="Pick the start date" floatingLabelText="Start Day"/&gt;
    );
  }
  </code></pre>
  
  <p>And here is my <code>updateStartDate</code> function where I'm just logging the output:</p>
  
  <pre><code>updateStartDate(event) {
     console.log('change start date', event);
  }
  </code></pre>
  
  <p>The only thing I get is this: <code>change start date {preventDefault: ƒ}</code> in the console. I've had other instances with a <code>TextField</code> where <code>onChange</code> gave me what I wanted, but not in this instance. Am I doing something wrong here?</p>