NullPointerException in ClassList.loadClassList when context class loader is unavailable in current thread.

[Htarlov]

Describe the bug
If we try to use Jep from a thread that has context class loader null (e.g. thread created from the outside of Java runtime) it fails with java.lang.NullPointerException at line 282 in ClassList in method loadClassList.

To Reproduce
Not yet have code to reproduce. A possible way similar to what we try to do:

• install Ant Media Server community
• git clone sample plugins https://github.com/ant-media/Plugins/
• open SamplePlugin with Eclipse JEE with Maven
• add Jep as dependency and try to instantiate it from f.ex. packet listener https://github.com/ant-media/Plugins/blob/master/SamplePlugin/src/main/java/io/antmedia/app/SamplePacketListener.java in onAudioPacket in a standard default way

Expected behavior
Instance of the class should be created without exception.

Environment (please complete the following information):

• OS Ubuntu 18.04
• Python 3.8
• OpenJDK Runtime Environment (build 11.0.15+10-Ubuntu-0ubuntu0.18.04.1)
• Jep Version: 4.0.3, 3.8.2
• Python packages: numpy

Additional context
When Thread.currentThread().getContextClassLoader() returns null then that null is added to the list of class loaders and then code tries to call in = cl.getResourceAsStream(rsc); and fails. A null check is needed before adding a class loader to the list.

[ndjensen]

Fixed in Jep 4.1.0.