title: Setting a value for composite data when property is in a group
body: <p>I have a custom property in my custom control. The custom property is in the Field1 group and is called ClientID.   The group and the field are in my custom property definition.  I want to set it on page load.  So I do the following:</p>
  
  <pre><code>compositeData.Field1.ClientID = getClientId("Field1")
  </code></pre>
  
  <p>When I do do I get an error:</p>
  
  <p>'compositeData.Field1' is null</p>
  
  <p>But if I define a property off of the root called Field1_ClientID and do the following:</p>
  
  <pre><code>compositeData.Field1_ClientID = getClientId("Field1")
  </code></pre>
  
  <p>Then all works well.  How can I make use of groups in custom properties?</p>