diff --git a/src/main/kotlin/iofXml/JsonMarshal.kt b/src/main/kotlin/iofXml/JsonMarshal.kt
index b40884679..8ef1e2f1d 100644
--- a/src/main/kotlin/iofXml/JsonMarshal.kt
+++ b/src/main/kotlin/iofXml/JsonMarshal.kt
@@ -3,6 +3,7 @@ package iofXml
 import com.fasterxml.jackson.annotation.JsonInclude
 import com.fasterxml.jackson.databind.ObjectMapper
 import com.fasterxml.jackson.databind.SerializationFeature
+import com.fasterxml.jackson.databind.json.JsonMapper
 import java.util.Locale
 import java.util.TimeZone
 import kotlin.collections.HashMap
@@ -62,7 +63,6 @@ fun iofV2JsonToXml(json: String) = iofJsonToXml(json, "v2")
 internal fun iofJsonToXml(json: String, iofVersion: String = "v3"): String {
     val mapper = ObjectMapper()
     mapper.setTimeZone(TimeZone.getDefault())
-    //mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
     val tempJsonMap = mapper.readValue(json, HashMap::class.java)
 
     val mainKeys = tempJsonMap.keys
@@ -103,13 +103,13 @@ internal fun iofJsonToXml(json: String, iofVersion: String = "v3"): String {
  * @sample iofXml.JsonMarshalKtTest.marshalIofObjectToJson
  */
 fun marshalIofObjectToJson(obj: Any, prettyPrint: Boolean = true): String {
-    val mapper = ObjectMapper()
-    mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL) // Else all fields not set will be 'null'
+    val builder = JsonMapper.builder()
+        .serializationInclusion(JsonInclude.Include.NON_NULL)
     if (prettyPrint) {
-        mapper.enable(SerializationFeature.INDENT_OUTPUT)
+        builder.enable(SerializationFeature.INDENT_OUTPUT)
     }
+    val mapper = builder.build()
 
-    //mapper.enable(SerializationFeature.WRAP_ROOT_VALUE) // Problem: root will be UpperCamelCase (need lowerCamelCase)
     val className = nameFromJavaClass(obj.javaClass)
     val objectWithRoot = mapOf(className to obj)
 
diff --git a/src/main/kotlin/iofXml/Main.kt b/src/main/kotlin/iofXml/Main.kt
index b39e7af8e..b89f71c99 100755
--- a/src/main/kotlin/iofXml/Main.kt
+++ b/src/main/kotlin/iofXml/Main.kt
@@ -6,7 +6,7 @@ import java.io.StringWriter
 import jakarta.xml.bind.JAXBContext
 import jakarta.xml.bind.Marshaller
 
-private fun main() {
+fun main() {
     val file = File("src/test/resources/v2-examples/ResultList_example.xml").readText()
     val (obj, name, theClass) = unmarshalGenericIofV2(file)
     println(ObjectMapper().writeValueAsString(obj))
@@ -72,7 +72,7 @@ val classesV3 = listOf(
 /**
  * List of all names for all main classes of IOF V3 XSD specification, generated from [classesV3][classesV3].
  */
-val classNamesV3 = classesV3.map { nameFromJavaClass(it.javaClass) }
+val classNamesV3 = classesV3.map { nameFromJavaClass(it) }
 
 /**
  * List of all main types / classes of IOF V2 XSD specification. Only these
@@ -97,4 +97,4 @@ val classesV2 = listOf(
 /**
  * List of all names for all main classes of IOF V2 XSD specification, generated from [classesV2][classesV2].
  */
-val classNamesV2 = classesV2.map { nameFromJavaClass(it.javaClass) }
+val classNamesV2 = classesV2.map { nameFromJavaClass(it) }
diff --git a/src/main/kotlin/iofXml/V2Unmarshallers.kt b/src/main/kotlin/iofXml/V2Unmarshallers.kt
index 9b0395b8d..1f7820a54 100644
--- a/src/main/kotlin/iofXml/V2Unmarshallers.kt
+++ b/src/main/kotlin/iofXml/V2Unmarshallers.kt
@@ -1,7 +1,6 @@
 package iofXml
 
 import java.io.StringReader
-import java.lang.Class
 import jakarta.xml.bind.JAXBContext
 import javax.xml.parsers.SAXParserFactory
 import javax.xml.transform.sax.SAXSource
@@ -35,7 +34,7 @@ fun unmarshalGenericIofV2(xml: String): Triple<Any, String, Class<*>> {
         // Credit: https://stackoverflow.com/a/64931583/5550386
         val spf = SAXParserFactory.newInstance()
         // Do not validate DTD
-        spf.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
+        spf.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false)
         val xmlSource = SAXSource(
             spf.newSAXParser().xmlReader,
             InputSource(StringReader(xmlClean))
@@ -55,7 +54,7 @@ private fun unmarshalV2Xml(className: String, dirtyXml: String): Any {
     val xml = removeUTF8BOM(dirtyXml, mainElementName)
 
     if (mainElementName != className) {
-        println("ERROR V2: mainElementName=$mainElementName is not equal to className=$className")
+        throw IllegalArgumentException("V2: mainElementName=$mainElementName is not equal to className=$className")
     }
 
     val actualClass = Class.forName("iofXml.v2.$className")
@@ -69,7 +68,7 @@ private fun unmarshalV2Xml(className: String, dirtyXml: String): Any {
         // Credit: https://stackoverflow.com/a/64931583/5550386
         val spf = SAXParserFactory.newInstance()
         // Do not validate DTD
-        spf.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
+        spf.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false)
         val xmlSource = SAXSource(
             spf.newSAXParser().xmlReader,
             InputSource(StringReader(xml))
diff --git a/src/main/kotlin/iofXml/V3Unmarshallers.kt b/src/main/kotlin/iofXml/V3Unmarshallers.kt
index eb665da6d..09d6ee0bf 100644
--- a/src/main/kotlin/iofXml/V3Unmarshallers.kt
+++ b/src/main/kotlin/iofXml/V3Unmarshallers.kt
@@ -1,7 +1,6 @@
 package iofXml
 
 import java.io.StringReader
-import java.lang.Class
 import java.net.URL
 import jakarta.xml.bind.JAXBContext
 import javax.xml.XMLConstants
@@ -45,7 +44,7 @@ private fun unmarshalV3Xml(className: String, dirtyXml: String, validateXml: Boo
     val mainElementName = getMainElementName(dirtyXml) ?: ""
     val xml = removeUTF8BOM(dirtyXml, mainElementName)
     if (mainElementName != className) {
-        println("ERROR V3: mainElementName=$mainElementName is not equal to className=$className")
+        throw IllegalArgumentException("V3: mainElementName=$mainElementName is not equal to className=$className")
     }
 
     val actualClass = Class.forName("iofXml.v3.$className")
diff --git a/src/test/kotlin/iofXml/V2UnmarshallersKtTest.kt b/src/test/kotlin/iofXml/V2UnmarshallersKtTest.kt
index eec114b50..8455dd42b 100644
--- a/src/test/kotlin/iofXml/V2UnmarshallersKtTest.kt
+++ b/src/test/kotlin/iofXml/V2UnmarshallersKtTest.kt
@@ -14,7 +14,7 @@ internal class V2UnmarshallersKtTest {
         val (obj) = unmarshalGenericIofV2(file)
         val xmlString = marshallIofObject(obj)
 
-        assert(xmlString.length > 0)
+        assert(xmlString.isNotEmpty())
         assert(xmlString.contains("<PersonName>"))
         assert(xmlString.contains("Ejsing"))
     }