[core] fix toXml for UnparsedIQ

smack-core/src/main/java/org/jivesoftware/smack/packet/UnparsedIQ.java

@@ -16,6 +16,8 @@
  */
 package org.jivesoftware.smack.packet;
 
+import org.jivesoftware.smack.util.StringUtils;
+
 /**
  * An IQ stanzas that could not be parsed because no provider was found.
  */
@@ -34,7 +36,12 @@ public class UnparsedIQ extends IQ {
 
     @Override
     protected IQChildElementXmlStringBuilder getIQChildElementBuilder(IQChildElementXmlStringBuilder xml) {
-        xml.escape(content);
+        if (StringUtils.isEmpty(content)) {
+            xml.setEmptyElement();
+        } else {
+            xml.rightAngleBracket();
+            xml.escape(content);
+        }
         return xml;
     }
 }

smack-core/src/test/java/org/jivesoftware/smack/packet/IqTest.java

@@ -58,4 +58,19 @@ public class IqTest {
         IQ iq = PacketParserUtils.parseIQ(parser);
         assertXmlSimilar(iqXml, iq.toXML());
     }
+
+    @ParameterizedTest
+    @EnumSource(SmackTestUtil.XmlPullParserKind.class)
+    public void testUnparsedIq(SmackTestUtil.XmlPullParserKind parserKind) throws Exception {
+        final String iqXml = "<iq xmlns='jabber:client' type='get' id='test-1'>" +
+                        "<query xmlns='jabber:iq:version'/>" +
+                        "</iq>";
+        final String expected = "<iq xmlns='jabber:client'  id='test-1' type='get'>"
+                         + "<query xmlns='jabber:iq:version'>&lt;query xmlns=&apos;jabber:iq:version&apos;/&gt;</query>"
+                         + "</iq>";
+
+        XmlPullParser parser = SmackTestUtil.getParserFor(iqXml, "iq", parserKind);
+        IQ iq = PacketParserUtils.parseIQ(parser);
+        assertXmlSimilar(expected, iq.toXML());
+    }
 }