title: making a multiple checkbox sticky
body: <p>I have a form which I want to make sticky. It has lots of check boxes:</p>
  
  <pre><code>&lt;label&gt;&lt;span&gt;ASD&lt;/span&gt;&lt;/label&gt;&lt;input type="checkbox"  name="condition[]" value="ASD" &lt;?php if (in_array("ASD", $_POST['condition'])) echo 'checked'; ?&gt; /&gt;&lt;br /&gt;
  &lt;label&gt;&lt;span&gt;SLC&lt;/span&gt;&lt;/label&gt;&lt;input type="checkbox"  name="condition[]" value="SLC" &lt;?php if (in_array("SLC", $_POST['condition'])) echo 'checked'; ?&gt; /&gt;&lt;br /&gt;...
  </code></pre>
  
  <p>Upon submit this works fine expect if the user makes no selection. I think this is something to do with the fact that the array is empty. I get an error:</p>
  
  <blockquote>
    <p>Undefined index: condition</p>
  </blockquote>
  
  <p>and also</p>
  
  <blockquote>
    <p>in_array() expects parameter 2 to be array, null</p>
  </blockquote>
  
  <p>thanks</p>