Can't run Vaadin sample project bootiful neo4-j

I am trying to run the Neo4J sample project here:

I can start it succcessfully via mvn spring-boot:run, but when I go to localhost:8080 I get this nice error message:

Failed to load the widgetset: ./VAADIN/widgetsets/org.vaadin.neo4j.vaadin.AppWidgetSet/org.vaadin.neo4j.vaadin.AppWidgetSet.nocache.js?1456179997254

I googled around and it looks like that I need to “compile the widget.” Yeah, ok.

I have the Vaadin plugin installed in Eclipse. When I right click on the AppWidgetSet.gwt.xml file and click on the gear icon
to compile it with the plugin, I get a nice NullPointerException:

at com.vaadin.integration.eclipse.builder.WidgetsetBuildManager.compileWidgetset(
at com.vaadin.integration.eclipse.handlers.CompileWidgetsetHandler.compileFile(
at com.vaadin.integration.eclipse.handlers.CompileWidgetsetHandler$

The pom.xml has an update-widgetset goal, but a comment says that is non-functional.