Deserialization of Java Bean not possible within an ivy Script Element

ivy 5.0.9

I created an Helper Class which should serialize / deserialize a Java Bean with the java.beans.XMLEncoder / XMLDecoder Class. Serialization works great, but if I want to deserialize the xml string within an Ivy Script Element, I got the following Error: java.lang.ArrayIndexOutOfBoundsException: 0

If I do the deserialization within the Helper Class itself (as described as follows), the deserialization works great. Is there a way to bring it working within the Ivy Script Step?

Thanks in advance for your ideas...

Helper Class "decode"

public Employee decode(String xml) {
    try {           
        XMLDecoder decoder = new XMLDecoder(IOUtils.toInputStream(xml, "UTF-8"));
        Employee employee = (Employee) decoder.readObject();
        decoder.close();
        return employee;
    } catch (Exception ex) {
        Ivy.log().error(ex.getMessage(), xml);
        return null;            
    }                       
}

Calling the method using Ivy Script Step (Not working)

import test.XmlHelper;
import test.Employee;
try {
    XmlHelper xh = new XmlHelper();
    in.employee = xh.decode(in.usrData); 
    /*
    (in.employee is a DataClass Attr. of type Employee
    in.usrData is a DataClass Attr. of type String containing the xml String)
    */
} catch (Exception ex) {
    in.errmsg = ex.getMessage();
}

Calling the method directly in the Helper Class by main method (Works great)

public static void main(String[] args) {        
    XmlHelper xh = new XmlHelper();     
    Employee employee = new Employee();
    employee = xh.decode("<java version='1.7.0_17' class='java.beans.XMLDecoder'><object class='test.Employee'><void property='firstName'><string>Vorname</string></void><void property='lastName'><string>Nachname</string></void>");
    System.out.println(employee.getFirstName());
    System.out.println(employee.getLastName());

}

Bean Employee (in ivy located under /src/test/entity )

package test.entity;

import java.io.Serializable;

public class Employee implements Serializable {         
private static final long serialVersionUID = 1L;
private String      lastname        = "";   
private String      firstname       = "";   
public String getLastName() {
    return lastname;
}
public void setLastName(String lastname) {
    this.lastname = lastname;
}
public String getFirstName() {
    return firstname;
}
public void setFirstName(String firstname) {
    this.firstname = firstname;
}

}