The issue can be reproduced on windows8 32bit with jdk9 b105 PIT build from:
http://jre.us.oracle.com/java/re/jdk/9/jdk9-client/103_2016-01-26-0302_4331/
To reproduce:
1. Open mentioned build and enable trace.
2. Try to load any applet in IE 11, like the one from
http://sqeweb.us.oracle.com/net/scanas415/export/deployment/larry/BAT/html/testDynamicVersion_131.html
3. If npe is thrown with trace like below the issue is reproduced:

basic: Added progress listener: sun.plugin.util.ProgressMonitorAdapter@dac28d
security: Expected Main URL: http://sqeweb.us.oracle.com/net/scanas415/export/deployment/larry/BAT/classes/CertSigned.jar
basic: exception: null.
java.lang.NullPointerException
at com.sun.deploy.util.SystemUtils.encodeString(Unknown Source)
at sun.plugin2.applet.Applet2Manager.getParametersString(Unknown Source)
at sun.plugin2.applet.Applet2Manager.getAppInfo(Unknown Source)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
at java.lang.Thread.run(Thread.java:804)