Index: /trunk/src/org/openstreetmap/josm/data/cache/JCSCacheManager.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/cache/JCSCacheManager.java	(revision 13671)
+++ /trunk/src/org/openstreetmap/josm/data/cache/JCSCacheManager.java	(revision 13672)
@@ -122,5 +122,5 @@
                         Logging.warn("Cannot lock cache directory. Will not use disk cache");
                 } catch (IOException e) {
-                    Logging.warn("Cannot create cache dir \"" + cacheDirLockPath.toString() + "\" lock file: " + e.toString());
+                    Logging.log(Logging.LEVEL_WARN, "Cannot create cache dir \"" + cacheDirLockPath + "\" lock file:", e);
                     Logging.warn("Will not use disk cache");
                 }
@@ -200,4 +200,5 @@
                 // in case any error in setting auxiliary cache, do not use disk cache at all - only memory
                 cc.setAuxCaches(new AuxiliaryCache[0]);
+                Logging.debug(e);
             }
         }
Index: /trunk/src/org/openstreetmap/josm/data/validation/OsmValidator.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/validation/OsmValidator.java	(revision 13671)
+++ /trunk/src/org/openstreetmap/josm/data/validation/OsmValidator.java	(revision 13672)
@@ -405,7 +405,7 @@
                 Logging.error(message);
                 if (!GraphicsEnvironment.isHeadless()) {
-                    GuiHelper.runInEDT(() -> {
-                        JOptionPane.showMessageDialog(Main.parent, message, tr("Error"), JOptionPane.ERROR_MESSAGE);
-                    });
+                    GuiHelper.runInEDT(() ->
+                        JOptionPane.showMessageDialog(Main.parent, message, tr("Error"), JOptionPane.ERROR_MESSAGE)
+                    );
                 }
             }
Index: /trunk/src/org/openstreetmap/josm/tools/WinRegistry.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/tools/WinRegistry.java	(revision 13671)
+++ /trunk/src/org/openstreetmap/josm/tools/WinRegistry.java	(revision 13672)
@@ -183,5 +183,5 @@
             throws IllegalAccessException, InvocationTargetException {
         if (regOpenKey == null || regQueryInfoKey == null || regEnumValue == null || regCloseKey == null) {
-            return null;
+            return Collections.emptyMap();
         }
         HashMap<String, String> results = new HashMap<>();
@@ -189,5 +189,5 @@
         Object handles = regOpenKey.invoke(root, hkey(hkey), toCstr(key), Integer.valueOf(KEY_READ));
         if (getNumber(handles, 1).longValue() != REG_SUCCESS) {
-            return null;
+            return Collections.emptyMap();
         }
         // Need to capture both int[] (Java 8-10) and long[] (Java 11+)
@@ -208,5 +208,5 @@
             throws IllegalAccessException, InvocationTargetException {
         if (regOpenKey == null || regQueryInfoKey == null || regEnumKeyEx == null || regCloseKey == null) {
-            return null;
+            return Collections.emptyList();
         }
         List<String> results = new ArrayList<>();