"Classpath is incomplete" warning with Maven project

I get the "Classpath is incomplete" popup warning, but can't seem to figure out the magic combination of rain dances required to make it "work".

Environment

• Operating System: Mac OS 10.13.6
• JDK version: 1.8.0_144
• Visual Studio Code version: 1.27.2
• Java extension version: 0.3.0

Steps To Reproduce

1. Create a blank maven project in an empty folder using the context menu "Generate from Maven Archetype"
2. Open the generated App.java

Sample project attached
threadtest.zip

The only relevant log entry in server log is:

!ENTRY org.eclipse.jdt.ls.core 1 0 2018-09-27 11:53:20.416
!MESSAGE Classpath is incomplete. Only syntax errors will be reported for file:///<REDACTED>/threadtest/src/main/java/threadtest/App.java

Current Result

VS Code pops up the "Classpath is incomplete" warning

Expected Result

Based on the suggestions here, I expected to not get this warning. It's worth noting however, that the language on this page is a little confusing. Particularly this:

Whenever a java file is opened, that does not belong to a project

VS Code doesn't have a concept of a "project". Are you talking about a Maven project? Folks new to either VS Code or your extension (like me) might be confused by what this means (in-fact I am still confused, because I think I have a project but presumably I don't)

Comienza con el threadtest.zip adjunto y el App.java generado; después, compara la entrada del registro del servidor con las indicaciones enlazadas sobre la advertencia “Classpath is incomplete”. Reproduce la advertencia usando, si están disponibles, las versiones indicadas de VS Code, la Java extension, JDK y macOS; se considera terminado cuando el proyecto Maven vacío se abre sin el popup.