t:popup - Null pointer exception.

[Sloan, Noah M]

Can anyone tell me why:

<t:popup styleClass="popup"
    closePopupOnExitingElement="false"
    closePopupOnExitingPopup="true"
    displayAtDistanceX="0"
    displayAtDistanceY="0">
  <h:outputText value="Value1" />
 <f:facet name="String">
  <h:panelGroup>
   <h:panelGrid columns="1">
    <h:outputText value="Value2" />       
   </h:panelGrid>
  </h:panelGroup>
 </f:facet>
</t:popup>


Gives me:

java.lang.NullPointerException
 at 
org.apache.myfaces.renderkit.RendererUtils.renderChildren(RendererUtils.java:422)
 at 
org.apache.myfaces.custom.popup.HtmlPopupRenderer.encodeEnd(HtmlPopupRenderer.java:92)
 at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:720)
 at 
com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:443)
 at 
com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:440)
 at 
com.sun.faces.renderkit.html_basic.GridRenderer.encodeChildren(GridRenderer.java:233)
 at 
javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:701)

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