Can't Compile WidgetSet - Vaadin 7 Java 12

When we try to build our UI it fails when trying to compile the widgetset. We just switched from Java 8 to 12. We are building with Gradle 5. Any help would be appreciated.

Looks like a transitive dependency has changed.

Error Log:
Compiling module com.dmb.ui.widgetset.Ui_projectWidgetset
Hint: Check that your module inherits ‘’ either directly or indirectly (most often by inheriting module ‘’)

Build Output:

Task :ManagerUI:vaadinCompile FAILED

FAILURE: Build failed with an exception.

  • What went wrong:
    Execution failed for task ‘:ManagerUI:vaadinCompile’.

Widgetset failed to compile. See error log.

— boilerplate output —

BUILD FAILED in 1m 29s
71 actionable tasks: 32 executed, 39 up-to-date

org.gradle.internal.exceptions.LocationAwareException: Execution failed for task ‘:ManagerUI:vaadinCompile’.

I’m betting that I need to find out which version of GWT Vaadin 7.7.9 (what we are using) needs. Luckily we will soon be upgrading to Vaadin 13 or newer.

Vaadin 7.7.9 was depending on GWT 2.7.0 which does not contain the class that the WidgetSetCompiler is looking for. Why this only shows up when you build with Java 12 I don’t know.