Custom WidgetSet ClassCastException

A little background first. I am writing a standalone application running on embedded jetty. It is not compiled as a war, but does deploy a WebContent folder with VAADIN and WEB-INF (with a web.xml for use in embedded jetty running alongside a guice container). Currently this is using vaadin 7.4.4 and Java 1.7. All other features are currently working in this configuration.

Right now, I want to add a custom renderer (call it for now a currency renderer). I cannot use the one present in the add-ons as that was built for 6.0 and I am taking the opportunity to figure out the under-the-covers items of vaadin/gwt. Based on the basics I know ...

• created a CurrencyRenderer.java that extends import com.vaadin.ui.Grid.AbstractRenderer
• created a CurrencyRendererWidgetset.gwt.xml with

<module>
   <inherits name="com.vaadin.DefaultWidgetSet" />
   <inherits name="com.google.gwt.resources.Resources" />
</module>

• created a client component CurrencyRendererClient which inherits import com.vaadin.client.renderers.Renderer
• created a connector class to put these all together

@Connect(CurrencyRenderer.class)
public class CurrencyRendererConnector extends AbstractRendererConnector<Currency> {
  @Override
  public CurrencyRendererClient getRenderer() {
    return (CurrencyRendererClient) super.getRenderer();
  }
}

• compile the gwt widgetset, put into WebContent/VAADIN/widgetsets deployed
• compile the jars and placed into WebContent/WEB-INF/lib

So, when I run this and try to use it in a vaadin grid, I get the following error (via Chrome javascript debugger, no error on the server):

Tue Jun 16 05:50:06 GMT-600 2015 com.vaadin.client.ApplicationConnection
SEVERE: Error sending state change eventscom.google.gwt.event.shared.UmbrellaException: Exception caught: undefined
    at Unknown.Eg(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.Ig(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.Og(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.Ex(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.Hx(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.cx(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.IAb(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.WAb(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.Ywb(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.Swb(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.cwb(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.awb(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.Dxb(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.Jx(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.ey(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.eval(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.li(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.oi(com.vaadin.DefaultWidgetSet-0.js)
    at Unknown.eval(com.vaadin.DefaultWidgetSet-0.js)
Caused by: java.lang.ClassCastException
   ...

Clearly I missed something in a step to create custom widgets, but I am not sure what. Anyone know or have a good custom widgetset guide? The vaadin one is missing some items about creating when not using the eclipse plugin.