/usr/lib/jvm/java-11-openjdk-amd64/demo/nbproject is in openjdk-11-demo 10.0.1+10-3ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/jvm/java-11-openjdk-amd64/demo/../../../../share/doc/openjdk-11-jre-headless/demo/nbproject