ThreadLocal leak in com.vaadin.sass.internal.handler.SCSSErrorHandler?

Since upgrading to Vaadin 8, we’ve started seeing our web application fail to undeploy from Tomcat. This is the message being logged:

The web application [ROOT]
created a ThreadLocal with key of type [java.lang.ThreadLocal]
(value [java.lang.ThreadLocal@ab3286d]
) and a value of type [com.vaadin.sass.internal.handler.SCSSErrorHandler]
(value [com.vaadin.sass.internal.handler.SCSSErrorHandler@23205ff9]
) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.

Looking at the SCSSErrorHandler class, it looks like it creates a ThreadLocal, though I can’t spot where it might be removed later.