Index: src/org/openstreetmap/josm/gui/tagging/presets/TaggingPresets.java
===================================================================
--- src/org/openstreetmap/josm/gui/tagging/presets/TaggingPresets.java	(revision 18275)
+++ src/org/openstreetmap/josm/gui/tagging/presets/TaggingPresets.java	(working copy)
@@ -204,13 +204,13 @@
     /**
      * Return set of values for a key in the tagging presets
      * @param key the key
-     * @return set of values for a key in the tagging presets or null if none is found
+     * @return set of values for a key in the tagging presets
      */
     public static Set<String> getPresetValues(String key) {
         Set<String> values = PRESET_TAG_CACHE.get(key);
         if (values != null)
             return Collections.unmodifiableSet(values);
-        return null;
+        return Collections.emptySet();
     }

     /**
Index: src/org/openstreetmap/josm/data/validation/tests/TagChecker.java
===================================================================
--- src/org/openstreetmap/josm/data/validation/tests/TagChecker.java	(revision 18275)
+++ src/org/openstreetmap/josm/data/validation/tests/TagChecker.java	(working copy)
@@ -545,7 +545,7 @@
      */
     private static Set<String> getPresetValues(String key) {
         Set<String> res = TaggingPresets.getPresetValues(key);
-        if (res != null)
+        if (!Utils.isEmpty(res))
             return res;
         if (additionalPresetsValueData.contains(key))
             return Collections.emptySet();
@@ -560,7 +560,7 @@
      * @since 9023
      */
     public static boolean isKeyInPresets(String key) {
-        return TaggingPresets.getPresetValues(key) != null;
+        return !Utils.isEmpty(TaggingPresets.getPresetValues(key));
     }

     /**
