The spec for System.getProperties
https://docs.oracle.com/javase/9/docs/api/java/lang/System.html#getProperties--
requires that java.class.path be always defined.

But https://docs.oracle.com/javase/9/docs/api/java/lang/ClassLoader.html says
"""
The class path used by the built-in system class loader is determined by the system property "java.class.path" during early initialization of the VM. If the system property is not defined,
"""

which appears to be contradictory.