Fix #103

src/main/java/com/fasterxml/jackson/dataformat/xml/ser/XmlBeanPropertyWriter.java

@@ -78,18 +78,32 @@ public void serializeAsField(Object bean, JsonGenerator jgen, SerializerProvider
         throws Exception
     {
         Object value = get(bean);
-
-        /* Hmmh. Does the default null serialization work ok here? For now let's assume
-         * it does; can change later if not.
+
+        /* 13-Feb-2014, tatu: As per [#103], default handling does not really
+         *   work here. Rather, we need just a wrapping and should NOT call
+         *   null handler, as it does not know what to do...
+         *   
+         *   Question, however, is what should it be serialized as. We have two main
+         *   choices; equivalent empty List, and "nothing" (missing). Let's start with
+         *   empty List? But producing missing entry is non-trivial...
          */
         if (value == null) {
-            if (_nullSerializer != null) {
-                jgen.writeFieldName(_name);
-                _nullSerializer.serialize(null, jgen, prov);
+            // if (_nullSerializer != null) { ... }
+
+            // For Empty List, we'd do this:
+            /*
+            @SuppressWarnings("resource")
+            final ToXmlGenerator xmlGen = (jgen instanceof ToXmlGenerator) ? (ToXmlGenerator) jgen : null;
+            if (xmlGen != null) {
+                xmlGen.startWrappedValue(_wrapperQName, _wrappedQName);
+                xmlGen.finishWrappedValue(_wrapperQName, _wrappedQName);
             }
+            */
+            // but for missing thing, well, just output nothing
+
             return;
         }
-        
+
         // then find serializer to use
         JsonSerializer<Object> ser = _serializer;
         if (ser == null) {
@@ -112,13 +126,16 @@ public void serializeAsField(Object bean, JsonGenerator jgen, SerializerProvider
         }
         // For non-nulls: simple check for direct cycles
         if (value == bean) {
-            _handleSelfReference(bean, ser);
+            // NOTE: method signature here change 2.3->2.4
+            if (_handleSelfReference(bean, jgen, prov, ser)) {
+                return;
+            }
         }
 
-        // Ok then; addition we want to do is to add wrapper element, and that's what happens here
-        // 19-Aug-2013, tatu: ... except for those nasty 'convertValue()' calls...
         @SuppressWarnings("resource")
         final ToXmlGenerator xmlGen = (jgen instanceof ToXmlGenerator) ? (ToXmlGenerator) jgen : null;
+        // Ok then; addition we want to do is to add wrapper element, and that's what happens here
+        // 19-Aug-2013, tatu: ... except for those nasty 'convertValue()' calls...
         if (xmlGen != null) {
             xmlGen.startWrappedValue(_wrapperQName, _wrappedQName);
         }

src/test/java/com/fasterxml/jackson/dataformat/xml/lists/TestWrappedLists.java

@@ -0,0 +1,41 @@
+package com.fasterxml.jackson.dataformat.xml.lists;
+
+import java.util.*;
+
+import com.fasterxml.jackson.dataformat.xml.XmlMapper;
+import com.fasterxml.jackson.dataformat.xml.XmlTestBase;
+import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlElementWrapper;
+import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;
+
+public class TestWrappedLists extends XmlTestBase
+{
+    static class Order  {
+        @JacksonXmlElementWrapper(localName = "line_items")
+        @JacksonXmlProperty(localName = "item")  
+        private List<ListItem> line_items; // new ArrayList<ListItem>();
+    }
+
+    static class ListItem {
+        public int id;
+
+        public ListItem(int id) { this.id = id; }
+    }
+
+    /*
+    /**********************************************************
+    /* Unit tests
+    /**********************************************************
+     */
+
+    private final XmlMapper MAPPER = xmlMapper(true);
+
+    /* For [Issue#103]
+     */
+    public void testEmptyList() throws Exception
+    {
+        String xml = MAPPER.writeValueAsString(new Order());
+        assertEquals("<Order/>", xml);
+        // If we expected Empty list, it'd be:
+//        assertEquals("<Order><line_items/></Order>", xml);
+    }
+}