Index: applications/editors/josm/plugins/validator/src/org/openstreetmap/josm/plugins/validator/tests/TagChecker.java
===================================================================
--- applications/editors/josm/plugins/validator/src/org/openstreetmap/josm/plugins/validator/tests/TagChecker.java	(revision 10530)
+++ applications/editors/josm/plugins/validator/src/org/openstreetmap/josm/plugins/validator/tests/TagChecker.java	(revision 10531)
@@ -568,4 +568,6 @@
 			sources = sb.substring(1);
 		}
+		if(sources.length() == 0)
+			sources = null;
 		Main.pref.put(PREF_SOURCES, sources );
 	}