EclipseLink Moxy unmarshall and getValueByXPath gives null - xpath

Question

I use the below code to get unmarshall and query the unmarshelled object by Xpath.
I am able to get the object after unmarshalling, but while querying by XPath, the value is coming as null.
Do I need to specify any NameSpaceResolver?
Please let me know if you are looking for any further information.
My code:
JAXBContext jaxbContext = (JAXBContext) JAXBContextFactory.createContext(new Class[] {Transaction.class}, null);
Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
StreamSource streamSource= new StreamSource(new StringReader(transactionXML));
transaction = unmarshaller.unmarshal(streamSource, Transaction.class).getValue();
String displayValue = jaxbContext.getValueByXPath(transaction, xPath, null, String.class);
My XML:
<Transaction xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" >
<SendingCustomer firstName="test">
</SendingCustomer>
</Transaction>

Answer 1

Since there are no namespaces in your example you do not need to worry about leveraging a NamespaceResolver. You didn't provide the XPath that you were having trouble with, so I have just picked one in the example below.
JAVA MODEL
Transaction
import javax.xml.bind.annotation.*;
#XmlRootElement(name="Transaction")
public class Transaction {
#XmlElement(name="SendingCustomer")
private Customer sendingCustomer;
}
Customer
import javax.xml.bind.annotation.XmlAttribute;
public class Customer {
#XmlAttribute
private String firstName;
#XmlAttribute
private String lastNameDecrypted;
#XmlAttribute(name="OnWUTrustList")
private boolean onWUTrustList;
#XmlAttribute(name="WUTrustListType")
private String wuTrustListType;
}
DEMO CODE
input.xml
<Transaction xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<SendingCustomer firstName="test" lastNameDecrypted="SMITH"
OnWUTrustList="false" WUTrustListType="NONE">
</SendingCustomer>
</Transaction>
Demo
import javax.xml.bind.Unmarshaller;
import javax.xml.transform.stream.StreamSource;
import org.eclipse.persistence.jaxb.JAXBContext;
import org.eclipse.persistence.jaxb.JAXBContextFactory;
public class Demo {
public static void main(String[] args) throws Exception {
JAXBContext jaxbContext = (JAXBContext) JAXBContextFactory.createContext(new Class[] {Transaction.class}, null);
Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
StreamSource streamSource= new StreamSource("src/forum17687460/input.xml");
Transaction transaction = unmarshaller.unmarshal(streamSource, Transaction.class).getValue();
String displayValue = jaxbContext.getValueByXPath(transaction, "SendingCustomer/#firstName", null, String.class);
System.out.println(displayValue);
}
}
Output
test