Fixed #493

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -4,6 +4,11 @@ Project: jackson-dataformat-xml
 === Releases ===
 ------------------------------------------------------------------------
 
+2.13.1 (not yet released)
+
+#493: SequenceWriter returns NPE when trying XML serialization
+ (reported by Moribund7@github)
+
 2.13.0 (30-Sep-2021)
 
 #441: Add `ToXmlGenerator.Feature.UNWRAP_ROOT_OBJECT_NODE` (to avoid

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

@@ -149,10 +149,14 @@ public void serializeValue(JsonGenerator gen, Object value, JavaType rootType,
             }
             QName rootName = _rootNameFromConfig();
             if (rootName == null) {
-                rootName = _rootNameLookup.findRootName(rootType, _config);
+                rootName = (rootType == null)
+                        ? _rootNameLookup.findRootName(value.getClass(), _config)
+                        : _rootNameLookup.findRootName(rootType, _config);
             }
             _initWithRootName(xgen, rootName);
-            asArray = TypeUtil.isIndexedType(rootType);
+            asArray = (rootType == null)
+                    ? TypeUtil.isIndexedType(value.getClass())
+                        : TypeUtil.isIndexedType(rootType);
             if (asArray) {
                 _startRootArray(xgen, rootName);
             }
@@ -194,10 +198,14 @@ public void serializePolymorphic(JsonGenerator gen, Object value, JavaType rootT
         } else {
             QName rootName = _rootNameFromConfig();
             if (rootName == null) {
-                rootName = _rootNameLookup.findRootName(rootType, _config);
+                rootName = (rootType == null)
+                        ? _rootNameLookup.findRootName(value.getClass(), _config)
+                        : _rootNameLookup.findRootName(rootType, _config);
             }
             _initWithRootName(xgen, rootName);
-            asArray = TypeUtil.isIndexedType(rootType);
+            asArray = (rootType == null)
+                    ? TypeUtil.isIndexedType(value.getClass())
+                    : TypeUtil.isIndexedType(rootType);
             if (asArray) {
                 _startRootArray(xgen, rootName);
             }

src/test/java/com/fasterxml/jackson/dataformat/xml/misc/SequenceWrite493Test.java

@@ -0,0 +1,29 @@
+package com.fasterxml.jackson.dataformat.xml.misc;
+
+import java.io.*;
+import java.util.HashMap;
+import java.util.Map;
+
+import com.fasterxml.jackson.databind.SequenceWriter;
+import com.fasterxml.jackson.dataformat.xml.XmlMapper;
+import com.fasterxml.jackson.dataformat.xml.XmlTestBase;
+
+public class SequenceWrite493Test extends XmlTestBase
+{
+    private final XmlMapper MAPPER = newMapper();
+
+    public void testIssue493() throws Exception
+    {
+        try (Writer w = new StringWriter()) {
+            SequenceWriter seqWriter = MAPPER.writer().writeValues(w);
+        
+            Map<String, String> reportObject = new HashMap<>();
+            reportObject.put("a", "b");
+            seqWriter.write(reportObject);
+
+            seqWriter.close();
+
+            assertEquals("<HashMap><a>b</a></HashMap>", w.toString().trim());
+        }
+    }
+}