Regression: Some invalid scenarios are throwing java.lang.NullPointerException

While evaluating the PIT automated results I noticed that some of the applets are failing, since instead of expected "NoClassDefFoundError " following exception is getting thrown
java.lang.NullPointerException
at sun.plugin2.applet.Plugin2Manager.findAppletJDKLevel(Unknown Source)
at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Exception: java.lang.NullPointerException

Steps to reproduce:
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1) Install 6u18-b04 pit and try to load following applet
http://sqeweb.sfbay.sun.com/deployment2/jitu/deployment_mustang_exec_ws/deployment/src/plugin/jarcaching/jarcaching/html/JarCachingNoHelperJarArchiveTest.html

If above mentioned exception is thrown instead of NoClassDefFoundError then bug is reproduced