I didn't put 'ErraiApp.properties' into 'widgets' module. Could you may be add some notes to the chapters 3 (Dependency Injection) and 6 (Errai CDI) of the reference which say that it doesn't work without 'ErraiApp.properties'? Because it not written that this file is required up until chapter 8.
Thanks for the suggestion. I've added callouts in chapters 2 and 6 with links to the ErraiApp.properties section in chapter 8.