NPE in DefaultPrefService.put

[ctrueden]

When running File > Export > Image... today:

[ERROR] Module threw exception
java.lang.NullPointerException
	at java.util.prefs.AbstractPreferences.put(AbstractPreferences.java:241)
	at org.scijava.prefs.DefaultPrefService$SmartPrefs.put(DefaultPrefService.java:393)
	at org.scijava.prefs.DefaultPrefService.put(DefaultPrefService.java:115)
	at org.scijava.module.DefaultModuleService.save(DefaultModuleService.java:306)
	at org.scijava.module.process.SaveInputsPreprocessor.saveValue(SaveInputsPreprocessor.java:77)
	at org.scijava.module.process.SaveInputsPreprocessor.process(SaveInputsPreprocessor.java:68)
	at org.scijava.module.ModuleRunner.preProcess(ModuleRunner.java:105)
	at org.scijava.module.ModuleRunner.run(ModuleRunner.java:157)
	at org.scijava.module.ModuleRunner.call(ModuleRunner.java:127)
	at org.scijava.module.ModuleRunner.call(ModuleRunner.java:66)
	at org.scijava.thread.DefaultThreadService$3.call(DefaultThreadService.java:238)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)