--- old/src/java.base/share/classes/java/time/format/DateTimeFormatter.java	2016-10-07 20:49:46.000000000 +0000
+++ new/src/java.base/share/classes/java/time/format/DateTimeFormatter.java	2016-10-07 20:49:46.000000000 +0000
@@ -1685,6 +1685,7 @@
     public DateTimeFormatter withResolverFields(TemporalField... resolverFields) {
         Set<TemporalField> fields = null;
         if (resolverFields != null) {
+            // Set.of cannot be used because it is hostile to nulls and duplicate elements
             fields = Collections.unmodifiableSet(new HashSet<>(Arrays.asList(resolverFields)));
         }
         if (Objects.equals(this.resolverFields, fields)) {