title: React warns about missing key on anonymous div wrapper with key'ed children
body: <p>Given this code, React throws a warning that there's no unique key specified on the wrapping <code>div</code>, although it shouldn't be needed as all child components have keys specified.</p>
  
  <pre><code>class exampleComponent extends React.Component {
    render() {
      return (
        &lt;div&gt;
          {this.state.data.map(({uniqueId, xData}) =&gt; {
            const bar = xData.map(({id}) =&gt; (
              &lt;X key={id}/&gt;
            ));
  
            const foo = &lt;foo key={uniqueId}/&gt;;
  
            return (
              &lt;div&gt; { /* No key in here, as it's not needed. Throws a warning */}
                {foo}
                {bar}
              &lt;/div&gt;
            );
  
          });
          }
        &lt;/div&gt;
      );
  
    }
  }
  </code></pre>