title: Primefaces selectonemenu on string check null value
body: <p>I want to render a panelgroup only if the value of my selectOneMenu is not null.
  I have this:</p>
  
  <pre><code>&lt;h:selectOneMenu value="#{bean.myString}"&gt;
      &lt;f:selectItem itemValue=#{null} itemLabel="None" /&gt;
      &lt;f:selectItem itemValue="first" itemLabel="First" /&gt;
      &lt;f:selectItem itemValue="second" itemLabel="Second" /&gt;
      &lt;f:ajax render="panelWrap" /&gt;
  &lt;/h:selectOneMenu&gt;
  
  &lt;h:panelGroup id="panelWrap"&gt;
      &lt;h:panelGroup rendered="#{bean.myString == null ? false : true}"&gt;
          // My content
      &lt;/h:panelGroup&gt;
  &lt;/h:panelGroup&gt;
  </code></pre>
  
  <p>I did this a lot with objects but here I am stuck on a simple string value.
  Can anybody help?
  Thanks</p>