title: Exception: source is null for getProperty(null, "agent")
body: <p>I am just learning how to use tapestry and I keep coming across the following error</p>
  
  <pre><code>Exception: source is null for getProperty(null, "agent")    
  ognl.OgnlRuntime.getProperty(OgnlRuntime.java:2203)
  </code></pre>
  
  <p>This is the code in my html page</p>
  
  <pre><code>&lt;tr&gt;
            &lt;td valign="center" align="right" height="30"&gt;&lt;span class="label1"&gt; &lt;span key="agentDeletionSalesParentActivityType" /&gt;&amp;nbsp;:&amp;nbsp;&lt;/span&gt;&lt;/td&gt;
            &lt;td valign="center" align="left" height="30"&gt;&lt;select jwcid="agentDeletionSalesParentActivityType@ActivityTypePropertySelection" regions="ognl:{activity.agent.region}" emptyOption="true" disabled="ognl:disabled" value="ognl:parentActivityType" /&gt;&lt;/td&gt;
          &lt;/tr&gt;
            &lt;tr&gt;
              &lt;td valign="center" align="right" height="30"&gt;&lt;span class="label1"&gt; &lt;span key="agentDeletionSalesChildActivityType" /&gt;&amp;nbsp;:&amp;nbsp;&lt;/span&gt;&lt;/td&gt;
              &lt;td valign="center" align="left" height="30"&gt;&lt;select jwcid="agentDeletionSalesChildActivityType" regions="ognl:{activity.agent.region}" emptyOption="true" disabled="ognl:disabled" value="ognl:childActivityType" parent="component:agentDeletionSalesParentActivityType" /&gt;&lt;/td&gt;
            &lt;/tr&gt;
  </code></pre>
  
  <p>This is my java code</p>
  
  <pre><code>@Persist
  public abstract ActivityType getParentActivityType();
  public abstract void setParentActivityType(ActivityType parent);
  
  @Persist
  public abstract ActivityType getChildActivityType();
  public abstract void setChildActivityType(ActivityType child);
  
  @Component(id="agentDeletionSalesChildActivityType", type="ActivityTypePropertySelection")
  public abstract ActivityTypePropertySelection getChildActivityPropertySelection();
  </code></pre>
  
  <p>If you need more code i will be happy to put it up (kept it small so as not to pile code into the page), can anyone see why this is returning this exception?</p>