Throuble with the new VAADIN 14 resource location

### ERROR when using vaadin 14 + spring boot 2 in Production MODE

IT seems SPRING can´t find CSS file in production.

2019-11-26 16:21:02.035 DEBUG 6944 --- [nio-8080-exec-7] o.s.web.servlet.DispatcherServlet : GET "/frontend-es6/com/github/appreciated/app-layout/app-layout-styles-lumo.css", parameters={}
2019-11-26 16:21:02.035 DEBUG 6944 --- [nio-8080-exec-7] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped to org.springframework.web.servlet.mvc.ServletForwardingController@1d97afdc
2019-11-26 16:21:02.051 DEBUG 6944 --- [nio-8080-exec-7] o.s.web.servlet.DispatcherServlet : Completed 404 NOT_FOUND
2019-11-26 16:21:02.051 DEBUG 6944 --- [nio-8080-exec-8] o.s.web.servlet.DispatcherServlet : GET "/frontend-es6/com/github/appreciated/app-layout/left/left-responsive-hybrid.css", parameters={}
2019-11-26 16:21:02.051 DEBUG 6944 --- [nio-8080-exec-8] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped to org.springframework.web.servlet.mvc.ServletForwardingController@1d97afdc
2019-11-26 16:21:02.067 DEBUG 6944 --- [nio-8080-exec-8] o.s.web.servlet.DispatcherServlet : Completed 404 NOT_FOUND

DOES NOT happens when using in DEBUG MODE

2019-11-26 17:32:38.367 DEBUG 6444 --- [nio-8080-exec-2] o.s.web.servlet.DispatcherServlet : GET "/frontend/com/github/appreciated/app-layout/app-layout-styles-lumo.css", parameters={}
2019-11-26 17:32:38.382 DEBUG 6444 --- [nio-8080-exec-2] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped to org.springframework.web.servlet.mvc.ServletForwardingController@e31a27
2019-11-26 17:32:38.601 DEBUG 6444 --- [nio-8080-exec-3] o.s.web.servlet.DispatcherServlet : GET "/frontend/com/github/appreciated/app-layout/left/left-responsive-hybrid.css", parameters={}
2019-11-26 17:32:38.601 DEBUG 6444 --- [nio-8080-exec-3] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped to org.springframework.web.servlet.mvc.ServletForwardingController@e31a27
2019-11-26 17:32:38.679 DEBUG 6444 --- [nio-8080-exec-2] o.s.web.servlet.DispatcherServlet : Completed 200 OK
2019-11-26 17:32:38.710 DEBUG 6444 --- [nio-8080-exec-3] o.s.web.servlet.DispatcherServlet : Completed 200 OK
@linspinho linspinho added the question label now

Start by reproducing the Vaadin 14 + Spring Boot 2 application in production mode and compare the CSS requests handled by Spring's DispatcherServlet and SimpleUrlHandlerMapping with debug mode. The issue names the failing /frontend-es6 CSS paths and the working /frontend paths; done means the production CSS requests return successfully instead of 404.