diff --git a/merlin-core/src/main/kotlin/de/micromata/merlin/excel/BeanUtils.kt b/merlin-core/src/main/kotlin/de/micromata/merlin/excel/BeanUtils.kt
index f8924b3c..e6de61eb 100644
--- a/merlin-core/src/main/kotlin/de/micromata/merlin/excel/BeanUtils.kt
+++ b/merlin-core/src/main/kotlin/de/micromata/merlin/excel/BeanUtils.kt
@@ -81,7 +81,7 @@ object BeanUtils {
     fun getGetterMethod(clazz: Class<*>, fieldname: String): Method? {
         val methods: Array<Method> = getAllDeclaredGetters(clazz)
         for (m in methods) {
-            if (m.name == "get${fieldname.capitalize()}") {
+            if (m.name == "get${fieldname.replaceFirstChar { it.uppercase() }}") {
                 return m
             }
         }
diff --git a/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelColumnDef.kt b/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelColumnDef.kt
index 88b80382..3248be99 100644
--- a/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelColumnDef.kt
+++ b/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelColumnDef.kt
@@ -33,7 +33,7 @@ constructor(
      * If not given, [columnHeadname] in decapitalized form will be used.
      */
     var targetProperty: String? = null
-        get() = if (field != null) field else columnHeadname?.decapitalize()
+        get() = if (field != null) field else columnHeadname?.replaceFirstChar { it.lowercase() }
         private set
 
     /**
diff --git a/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelRow.kt b/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelRow.kt
index 9303fcbf..f8d4584c 100644
--- a/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelRow.kt
+++ b/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelRow.kt
@@ -193,7 +193,7 @@ class ExcelRow(val sheet: ExcelSheet, val row: Row) {
                 continue
             }
             for (alias in colDef.columnAliases) {
-                searchResult = getPropertyValue(obj, colDef, alias.decapitalize(), ignoreProperties)
+                searchResult = getPropertyValue(obj, colDef, alias.replaceFirstChar { it.lowercase() }, ignoreProperties)
                 if (searchResult != null) {
                     processPropertyValue(obj, searchResult, colDef, process)
                     break
@@ -253,7 +253,7 @@ class ExcelRow(val sheet: ExcelSheet, val row: Row) {
                 return PropertySearchResult(false, BeanUtils.getValue(obj, getter))
             }
         }
-        val field = BeanUtils.getDeclaredField(obj::class.java, identifier.decapitalize())
+        val field = BeanUtils.getDeclaredField(obj::class.java, identifier.replaceFirstChar { it.lowercase() })
         if (field != null) {
             sheet.cache.autoFillCache.foundPropertiesMap[colDef] = WorkingCache.Property(field)
             return PropertySearchResult(false, BeanUtils.getValue(obj, field))
diff --git a/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelSheet.kt b/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelSheet.kt
index 87a3e270..ae1b1214 100644
--- a/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelSheet.kt
+++ b/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelSheet.kt
@@ -103,7 +103,7 @@ class ExcelSheet internal constructor(val excelWorkbook: ExcelWorkbook, val poiS
                 }
                 for (listener in columnDef.getColumnListeners()!!) {
                     if (listener is ExcelColumnValidator) {
-                        if (columnDef._columnNumber < 0) {
+                        if (columnDef._columnNumber < 0 && listener.isRequired) {
                             addValidationError(createValidationErrorMissingColumnByName(columnDef.columnHeadname))
                         }
                     }
diff --git a/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelWorkbook.kt b/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelWorkbook.kt
index 48484a84..7b867502 100644
--- a/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelWorkbook.kt
+++ b/merlin-core/src/main/kotlin/de/micromata/merlin/excel/ExcelWorkbook.kt
@@ -20,12 +20,15 @@ private val log = KotlinLogging.logger {}
 /**
  * Wraps and enhances a POI workbook.
  */
+@Suppress("unused", "MemberVisibilityCanBePrivate")
 class ExcelWorkbook
-@JvmOverloads constructor(
+@JvmOverloads
+constructor(
     /**
      * Is used e. g. for getting number cell values as String.
      */
-    val locale: Locale = Locale.getDefault()
+    val locale: Locale = Locale.getDefault(),
+    workbook: Workbook? = XSSFWorkbook(),
 ) : AutoCloseable {
 
     lateinit var pOIWorkbook: Workbook
@@ -37,10 +40,10 @@ class ExcelWorkbook
     private var inputStream: InputStream? = null
     var filename: String? = null
 
-    val filenameExtension: String?
+    val filenameExtension: String
         get() = File(filename ?: "unkown.xlsx").extension
 
-    val filenameWithoutExtension: String?
+    val filenameWithoutExtension: String
         get() = File(filename ?: "unkown.xlsx").nameWithoutExtension
 
     var formulaEvaluator: FormulaEvaluator? = null
@@ -57,7 +60,7 @@ class ExcelWorkbook
         workbook: Workbook,
         locale: Locale = Locale.getDefault()
     )
-            : this(locale) {
+            : this(locale, null) {
         pOIWorkbook = workbook
     }
 
@@ -73,7 +76,7 @@ class ExcelWorkbook
         excelFile: File,
         locale: Locale = Locale.getDefault()
     )
-            : this(locale) {
+            : this(locale, null) {
         try {
             val fis = FileInputStream(excelFile)
             open(fis, excelFile.name)
@@ -93,12 +96,12 @@ class ExcelWorkbook
         filename: String,
         locale: Locale = Locale.getDefault()
     )
-            : this(locale) {
+            : this(locale, null) {
         open(inputStream, filename)
     }
 
     /**
-     * @param inputStream The input stream to read the Excel content from.
+     * @param byteArray Byte array to read the Excel content from.
      * @param filename    Only for logging purposes if any error occurs.
      */
     @JvmOverloads
@@ -107,10 +110,16 @@ class ExcelWorkbook
         filename: String,
         locale: Locale = Locale.getDefault()
     )
-            : this(locale) {
+            : this(locale, null) {
         open(byteArray.inputStream(), filename)
     }
 
+    init {
+        if (workbook != null) {
+            pOIWorkbook = workbook
+        }
+    }
+
     private fun open(inputStream: InputStream, filename: String) {
         this.filename = File(filename).name
         this.inputStream = inputStream
@@ -201,7 +210,7 @@ class ExcelWorkbook
      *
      * @see Workbook.cloneSheet
      */
-    fun cloneSheet(sheetNum: Int, name: String?): ExcelSheet? {
+    fun cloneSheet(sheetNum: Int, name: String?): ExcelSheet {
         val index = pOIWorkbook.numberOfSheets
         val poiSheet: Sheet = this.pOIWorkbook.cloneSheet(sheetNum)
         this.pOIWorkbook.setSheetName(index, name)
@@ -216,7 +225,7 @@ class ExcelWorkbook
     /**
      * Remove the sheet at the given position.
      *
-     * @param index
+     * @param idx
      * @return this for chaining.
      */
     fun removeSheetAt(idx: Int) {
diff --git a/merlin-core/src/main/kotlin/de/micromata/merlin/utils/BeanHelper.kt b/merlin-core/src/main/kotlin/de/micromata/merlin/utils/BeanHelper.kt
index 7db0cf04..fd6a572d 100644
--- a/merlin-core/src/main/kotlin/de/micromata/merlin/utils/BeanHelper.kt
+++ b/merlin-core/src/main/kotlin/de/micromata/merlin/utils/BeanHelper.kt
@@ -23,8 +23,6 @@
 package de.micromata.merlin.utils
 
 import de.micromata.merlin.excel.importer.ImportLogger
-import org.apache.commons.lang3.ArrayUtils
-import org.apache.commons.lang3.StringUtils
 import org.slf4j.LoggerFactory
 import java.lang.reflect.Method
 import java.lang.reflect.Modifier
@@ -32,6 +30,7 @@ import java.math.BigDecimal
 import java.math.BigInteger
 import java.time.LocalDate
 import java.time.LocalDateTime
+import java.util.*
 
 /**
  * Stores one imported object (e. g. MS Excel row as bean object). It also contains information about the status: New object or modified
@@ -40,23 +39,21 @@ import java.time.LocalDateTime
  * @author Kai Reinhard (k.reinhard@micromata.de)
  */
 object BeanHelper {
-    //private val log = LoggerFactory.getLogger(BeanHelper::class.java)
-
     @JvmStatic
     @JvmOverloads
     fun determineGetter(clazz: Class<*>, fieldname: String, onlyPublicGetter: Boolean = true): Method? {
-        val cap = StringUtils.capitalize(fieldname)
+        val cap = fieldname.replaceFirstChar { it.uppercase() }
         val methods: Array<Method> = getAllDeclaredMethods(clazz) ?: return null
         for (method in methods) {
             if (onlyPublicGetter && !Modifier.isPublic(method.modifiers)) {
                 continue
             }
             val matches =
-                    if (Boolean::class.javaPrimitiveType!!.isAssignableFrom(method.returnType)) {
-                        "is$cap" == method.name || "has$cap" == method.name || "get$cap" == method.name
-                    } else {
-                        "get$cap" == method.name
-                    }
+                if (Boolean::class.javaPrimitiveType!!.isAssignableFrom(method.returnType)) {
+                    "is$cap" == method.name || "has$cap" == method.name || "get$cap" == method.name
+                } else {
+                    "get$cap" == method.name
+                }
             if (matches) {
                 if (!method.isBridge) { // Don't return bridged methods (methods defined in interface or super class with different return type).
                     return method
@@ -73,7 +70,7 @@ object BeanHelper {
         var methods = cls.declaredMethods
         while (cls.superclass != null) {
             cls = cls.superclass
-            methods = ArrayUtils.addAll(methods, *cls.declaredMethods) as Array<Method>
+            methods += cls.declaredMethods
         }
         return methods
     }
@@ -88,7 +85,7 @@ object BeanHelper {
      */
     @JvmStatic
     fun determineSetter(clazz: Class<*>, fieldname: String): Method? {
-        val cap = fieldname.capitalize()
+        val cap = fieldname.replaceFirstChar { it.uppercaseChar() }
         val methods: Array<Method> = getAllDeclaredMethods(clazz) ?: return null
         for (method in methods) {
             if ("set$cap" == method.name && method.parameterTypes.size == 1) {