webpack-closure-compiler throws cryptic error (and solution)

webpack-closure-compiler was used to convert compiled js from ecma6 to ecma5 by neuroglancer.

How I found out
npm run build works, npm run build-min does not. Commenting out the ClosureCompiler worked.

The diagnosis
New machine, did not install java runtime. Concurrency (default) only works with java runtime installed.

The fix
install java run time on ubuntu by

sudo apt-get install openjdk-8-jdk

npm run build-min worked.