As mentioned on https://avatar-js.java.net/ page, currently JDK8 with nashorn cannot execute express module due problems related to changing __proto__ to undefined. The fix on the library side is simple:
node_modules/ejs/lib/ejs.js line 286
- options.__proto__ = options.locals;
+ if (options.locals) options.__proto__ = options.locals;
yet we need to run existing node.js application without modification and as such I'd like to propose a fix on the Nashorn side as well.