If logback jars (logback-claaic and logback-core) are located in endorsed libraries ( -Djava.endorsed.dirs) its not possible to use a logback configuration url that ends with groovy.

This is because of line 23 in ch.qos.logback.classic.util.EnvUtil

ClassLoader classLoader = EnvUtil.class.getClassLoader();

witch return null if called from endorsed libraries.

It should work if you change it to

ClassLoader classLoader = EnvUtil.class.getClassLoader();
if (classLoader == null)
classLoader = ClassLoader.getSystemClassLoader();

I have not been able to verify this fix since I am not able to build logback