It is currently not possible to build Tuleap with Node.js 12.x due to multiple issues. I spotted those a while ago but it is going to become more and more annoying because Node.js 12.x is becoming the default for mainstream distributions (such as Fedora 31).
Two issues spotted for now:
* our version of node-sass is broken on Node.js 12.x (easily fix, see gerrit #16700
* Gulp 3 is deprecated is broken and does not work on Node.js 12.x