Field usr_paths in ClassLoader not found

Question

I'm following a tutorial, which at some point use this code.

ClassLoader.class.getDeclaredField("usr_paths").

Why it throws exception

java.lang.NoSuchFieldException: usr_paths

Classloader class decompiled definition shows that is has.

private static String usr_paths[];

I'm using: java 12.0.1 2019-04-16 Java(TM) SE Runtime Environment (build 12.0.1+12) Java HotSpot(TM) 64-Bit Server VM (build 12.0.1+12, mixed mode, sharing)