InaccessibleObjectException when launching via Java 9 Webstart

[simon04]

JOSM does not start in the end! Tested using r12712=tested, r12885=latest. The stack trace for r12885=latest is as follows:

java.lang.reflect.InaccessibleObjectException: Unable to make private static native int[] java.util.prefs.WindowsPreferences.WindowsRegOpenKey(int,byte[],int) accessible: module java.prefs does not "opens java.util.prefs" to unnamed module @57a4fe17
	at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(Unknown Source)
	at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(Unknown Source)
	at java.base/java.lang.reflect.Method.checkCanSetAccessible(Unknown Source)
	at java.base/java.lang.reflect.Method.setAccessible(Unknown Source)
	at org.openstreetmap.josm.tools.Utils.lambda$setObjectsAccessible$0(Utils.java:1509)
	at java.base/java.security.AccessController.doPrivileged(Native Method)
	at org.openstreetmap.josm.tools.Utils.setObjectsAccessible(Utils.java:1507)
	at org.openstreetmap.josm.tools.WinRegistry.<clinit>(WinRegistry.java:64)
	at org.openstreetmap.josm.tools.PlatformHookWindows.getCurrentBuild(PlatformHookWindows.java:300)
	at org.openstreetmap.josm.gui.MainApplication.applyWorkarounds(MainApplication.java:1083)
	at org.openstreetmap.josm.gui.MainApplication.mainJOSM(MainApplication.java:933)
	at org.openstreetmap.josm.gui.MainApplication$2.processArguments(MainApplication.java:274)
	at org.openstreetmap.josm.gui.MainApplication.main(MainApplication.java:851)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.base/java.lang.reflect.Method.invoke(Unknown Source)
	at jdk.javaws@9/com.sun.javaws.Launcher.executeApplication(Unknown Source)
	at jdk.javaws@9/com.sun.javaws.Launcher.executeMainClass(Unknown Source)
	at jdk.javaws@9/com.sun.javaws.Launcher.doLaunchApp(Unknown Source)
	at jdk.javaws@9/com.sun.javaws.Launcher.run(Unknown Source)
	at java.base/java.lang.Thread.run(Unknown Source)

C:\Users\simon>java -version
java version "9"
Java(TM) SE Runtime Environment (build 9+181)
Java HotSpot(TM) 64-Bit Server VM (build 9+181, mixed mode)