Calling SyncEditorLayerIndex.groovy creates unneeded preferences file and then throws NPE doing so

[stoecker]

2018-10-30 18:43:15.956 INFO: Missing preference file '/root/.config/JOSM/preferences.xml'. Creating a default preference file.
Caught: java.lang.NullPointerException java.lang.NullPointerException
         at org.openstreetmap.josm.data.preferences.PreferencesWriter.write(PreferencesWriter.java:59)
         at org.openstreetmap.josm.data.Preferences.save(Preferences.java:359)
         at org.openstreetmap.josm.data.Preferences.save(Preferences.java:333)
         at org.openstreetmap.josm.data.Preferences.putSetting(Preferences.java:598)
         at org.openstreetmap.josm.spi.preferences.AbstractPreferences.put(AbstractPreferences.java:25)
         at org.openstreetmap.josm.spi.preferences.AbstractPreferences.putInt(AbstractPreferences.java:55)
         at org.openstreetmap.josm.data.Preferences.save(Preferences.java:347)
         at org.openstreetmap.josm.data.Preferences.save(Preferences.java:333)
         at org.openstreetmap.josm.data.Preferences.init(Preferences.java:487)
         at org.openstreetmap.josm.data.Preferences$init.call(Unknown Source)
         at SyncEditorLayerIndex.main(SyncEditorLayerIndex.groovy:64)
         at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
         at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
         at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
         at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
         at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
         at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)