<p dir="auto">The CircularProgress.d.ts file does not have 'thickness' property.</p>


<ul class="contains-task-list">
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have searched the <a href="https://github.com/callemall/material-ui/issues">issues</a> of this repository and believe that this is not a duplicate.</li>
</ul>
<h2 dir="auto">Your Environment</h2>

<table role="table">
<thead>
<tr>
<th>Tech</th>
<th>Version</th>
</tr>
</thead>
<tbody>
<tr>
<td>Material-UI</td>
<td>1.0.0-beta.18</td>
</tr>
<tr>
<td>React</td>
<td>15.6.1</td>
</tr>
<tr>
<td>browser</td>
<td>Chrome 61.0.3163.100</td>
</tr>
</tbody>
</table>
<ul class="contains-task-list">
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have searched the <a href="https://github.com/callemall/material-ui/issues">issues</a> of this repository and believe that this is not a duplicate.</li>
</ul>
<h2 dir="auto">Expected Behavior</h2>
<p dir="auto">In the render method of a component, it would be convenient to be able to use boolean operators to decide whether or not a MenuItem child renders. E.g.:<br>
<code class="notranslate">&lt;Select&gt; &lt;MenuItem value=0 /&gt; &lt;MenuItem value=1 /&gt; {canBeTwo &amp;&amp; &lt;MenuItem value=2 /&gt;} &lt;/Select&gt; </code></p>
<h2 dir="auto">Current Behavior</h2>
<p dir="auto">At the moment, if canBeTwo is false in the exemple above, the following error message is returned:<br>
TypeError: Cannot read property 'props' of null at SelectInput.js:275 (Chrome)<br>
TypeError: child is null (Firefox)</p>
<h2 dir="auto">Steps to Reproduce (for bugs)</h2>
<p dir="auto"><a href="https://codesandbox.io/s/kkl9ypz7vo" rel="nofollow">live example</a></p>
<h2 dir="auto">Your Environment</h2>

<table role="table">
<thead>
<tr>
<th>Tech</th>
<th>Version</th>
</tr>
</thead>
<tbody>
<tr>
<td>Material-UI</td>
<td>v1 beta 10</td>
</tr>
<tr>
<td>React</td>
<td>15.6.1</td>
</tr>
<tr>
<td>browser</td>
<td>FF55 &amp; Chrome 58</td>
</tr>
</tbody>
</table>