Error compiling WidgetSet after upgrading 7.2.7 tp 7.7.8

After upgrading from Vaadin 7.2.7 to 7.7.8 I am receiving the following error while building my widgetset. Any help would be appreciated.

[java] Loading inherited module 'com.dbchk.vaadin.GRCWidgetSet'
     [java]    Loading inherited module 'com.vaadin.DefaultWidgetSet'
     [java]       Loading inherited module 'elemental.Json'
     [java]          [ERROR] Unable to find 'elemental/Json.gwt.xml' on your classpath; could be a typo, or maybe you forgot to include a classpath entry for source?

Have you used elemental.Json in your own code? This class is reserved purely for Vaadin internal use. In post 7.7. version client modules dependencies were also altered in the way that could cause this if you use elemental.Json in your own code.
 

I've searched the code and not found any references to it. This project was mostly developed by Vaadin for us so I don't know all the details of all the code.

The only results I see are inside vaadin-shared-7.7.8.jar.

What would I need to put on my classpath for the Widget compile to find the elemental/Json?
 

Is it possible that there is a missing Json.gwt.xml file in the vaadin-shared-7.7.8.jar file?

I solved this problem including the file gwt-elemental-2.7.0.vaadin6.jar