Index: trunk/src/org/openstreetmap/josm/data/notes/Note.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/notes/Note.java	(revision 17836)
+++ trunk/src/org/openstreetmap/josm/data/notes/Note.java	(revision 17837)
@@ -53,13 +53,9 @@
 
     /** Sorts notes by user, then creation date */
-    public static final Comparator<Note> USER_COMPARATOR = (n1, n2) -> {
-        String n1User = n1.getFirstComment().getUser().getName();
-        String n2User = n2.getFirstComment().getUser().getName();
-        return n1User.equals(n2User) ? DATE_COMPARATOR.compare(n1, n2) : n1User.compareTo(n2User);
-    };
+    public static final Comparator<Note> USER_COMPARATOR =
+            Comparator.comparing(Note::getUserName, Comparator.nullsLast(Comparator.naturalOrder())).thenComparing(DATE_COMPARATOR);
 
     /** Sorts notes by the last modified date */
-    public static final Comparator<Note> LAST_ACTION_COMPARATOR =
-            (n1, n2) -> NoteComment.DATE_COMPARATOR.compare(n1.getLastComment(), n2.getLastComment());
+    public static final Comparator<Note> LAST_ACTION_COMPARATOR = Comparator.comparing(Note::getLastComment, NoteComment.DATE_COMPARATOR);
 
     private long id;
@@ -181,4 +177,8 @@
     public NoteComment getFirstComment() {
         return comments.isEmpty() ? null : comments.get(0);
+    }
+
+    private String getUserName() {
+        return getFirstComment() == null ? null : getFirstComment().getUser().getName();
     }
 
Index: trunk/src/org/openstreetmap/josm/data/notes/NoteComment.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/notes/NoteComment.java	(revision 17836)
+++ trunk/src/org/openstreetmap/josm/data/notes/NoteComment.java	(revision 17837)
@@ -40,5 +40,5 @@
 
     /** Sorts note comments strictly by creation date */
-    public static final Comparator<NoteComment> DATE_COMPARATOR = Comparator.comparing(n -> n.commentTimestamp);
+    public static final Comparator<NoteComment> DATE_COMPARATOR = Comparator.nullsLast(Comparator.comparing(n -> n.commentTimestamp));
 
     /**