title: Gemfire cache "PDXInstance to Json" Joda DateTime error
body: <p>I am trying to get PDXInstances from the Gemfire cache and convert them to JSON but its failing when a Joda DateTime is encountered.</p>
  
  <p>Please see the error below -</p>
  
  <pre><code>Caused by: java.lang.IllegalStateException: PdxInstance returns unknwon pdxfield inServiceDate for type Fri Jun 18 00:00:00 CDT 1971
  </code></pre>
  
  <p>I am doing the below -</p>
  
  <pre><code>JSONFormatter.toJSON(pdxInstance)
  </code></pre>
  
  <p>Reference:
  <a href="http://pubs.vmware.com/vfabric53/index.jsp?topic=/com.vmware.vfabric.gemfire.7.0/developing/data_serialization/jsonformatter_pdxinstances.html" rel="nofollow">http://pubs.vmware.com/vfabric53/index.jsp?topic=/com.vmware.vfabric.gemfire.7.0/developing/data_serialization/jsonformatter_pdxinstances.html</a></p>
  
  <p>Anybody encountered this issue?</p>
  
  <p>Thanks</p>