From 6444f7afc393807fb4ac63a2c2911c5a70671b3f Mon Sep 17 00:00:00 2001
From: Alex Blekhman <ablekhman@atlassian.com>
Date: Mon, 27 Mar 2023 19:47:25 +1100
Subject: [PATCH] Fix AtomicReference marshalling. Closes #326.

---
 .../extended/AtomicReferenceConverter.java    | 28 +++++++++++--------
 .../acceptance/ConcurrentTypesTest.java       |  7 ++++-
 2 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/xstream/src/java/com/thoughtworks/xstream/converters/extended/AtomicReferenceConverter.java b/xstream/src/java/com/thoughtworks/xstream/converters/extended/AtomicReferenceConverter.java
index fb4638569..15d058a35 100644
--- a/xstream/src/java/com/thoughtworks/xstream/converters/extended/AtomicReferenceConverter.java
+++ b/xstream/src/java/com/thoughtworks/xstream/converters/extended/AtomicReferenceConverter.java
@@ -43,23 +43,29 @@ public boolean canConvert(final Class<?> type) {
     @Override
     public void marshal(final Object source, final HierarchicalStreamWriter writer, final MarshallingContext context) {
         final AtomicReference<?> ref = (AtomicReference<?>)source;
-        writer.startNode(mapper.serializedMember(AtomicReference.class, "value"));
-
         final Object object = ref.get();
-        final String name = mapper.serializedClass(object != null ? object.getClass() : null);
-        writer.addAttribute(mapper.aliasForSystemAttribute("class"), name);
-        context.convertAnother(ref.get());
-        writer.endNode();
+        if (object != null) {
+            writer.startNode(mapper.serializedMember(AtomicReference.class, "value"));
+
+            final String name = mapper.serializedClass(object.getClass());
+            writer.addAttribute(mapper.aliasForSystemAttribute("class"), name);
+            context.convertAnother(object);
+            writer.endNode();
+        }
     }
 
     @Override
     public Object unmarshal(final HierarchicalStreamReader reader, final UnmarshallingContext context) {
-        reader.moveDown();
+        if (reader.hasMoreChildren()) {
+            reader.moveDown();
 
-        final Class<?> type = HierarchicalStreams.readClassType(reader, mapper);
-        final Object value = context.convertAnother(context, type);
-        reader.moveUp();
-        return new AtomicReference<>(value);
+            final Class<?> type = HierarchicalStreams.readClassType(reader, mapper);
+            final Object value = context.convertAnother(context, type);
+            reader.moveUp();
+            return new AtomicReference<>(value);
+        } else {
+            return new AtomicReference<>();
+        }
     }
 
 }
diff --git a/xstream/src/test/com/thoughtworks/acceptance/ConcurrentTypesTest.java b/xstream/src/test/com/thoughtworks/acceptance/ConcurrentTypesTest.java
index 0d6d16246..e0e5cf4ee 100644
--- a/xstream/src/test/com/thoughtworks/acceptance/ConcurrentTypesTest.java
+++ b/xstream/src/test/com/thoughtworks/acceptance/ConcurrentTypesTest.java
@@ -108,12 +108,17 @@ public void testAtomicReference() {
 
     @SuppressWarnings("unchecked")
     public void testAtomicReferenceWithOldFormat() {
-        assertEquals(new AtomicReference<String>("test").get(), ((AtomicReference<String>)xstream.fromXML("" //
+        assertEquals(new AtomicReference<>("test").get(), ((AtomicReference<String>)xstream.fromXML("" //
             + "<java.util.concurrent.atomic.AtomicReference>\n" //
             + "  <value class='string'>test</value>\n" //
             + "</java.util.concurrent.atomic.AtomicReference>")).get());
     }
 
+    public void testEmptyAtomicReference() {
+        final AtomicReference<?> atomicRef = new AtomicReference<>();
+        assertBothWays(atomicRef, "<atomic-reference/>");
+    }
+
     public void testAtomicReferenceWithAlias() {
         xstream.aliasField("junit", AtomicReference.class, "value");
         final AtomicReference<String> atomicRef = new AtomicReference<>("test");