Unmarshalling dates using JAXB but getting nullpointer exception

Question

I am trying to convert XML to java object. In my xml, there is field which looks like:

<pickDisplayTs>2021-09-24T18:03:06.603 +0000</pickDisplayTs>

My Java object looks like the following:

@XmlElement(name = "pickDisplayTs" )
@XmlJavaTypeAdapter(DateAdapter.class)
public Date pickDisplayTs;

My DataAdapter class is the following:

    import javax.xml.bind.annotation.adapters.XmlAdapter;
    import java.text.SimpleDateFormat;
    import java.util.Date;

   public class DateAdapter extends XmlAdapter<String, Date> {

   private static final String CUSTOM_FORMAT_STRING = "yyyy-MM- 
   dd'T'HH:mm:ss.SSS'Z'";


    @Override
    public Date unmarshal(String v) throws Exception {
    return new SimpleDateFormat(CUSTOM_FORMAT_STRING).parse(v);
   }

@Override
public String marshal(Date v) throws Exception {
    return new SimpleDateFormat(CUSTOM_FORMAT_STRING).format(v);
}

}

Code reference: https://github.com/eugenp/tutorials/blob/950bbadc353bdca114befc98cf4a18476352220e/jaxb/src/main/java/com/baeldung/jaxb/dateunmarshalling/DateAdapter.java

This is the method for unmarshalling the xml file:

  String filepath = "xml/PickComplete.xml";
  String xmlPickComplete = readFromResources(filepath);
  PickComp pickCompleteMq = Xml.xmlToObject(xmlPickComplete, PickingSubSystemOrderCompleteMessage.class);

The entire pickCompleteMq is coming to be null but if I am declaring the pickDisplayTs as string, its all good, not sure where I am going wrong. But I need the field to be in Date.

Any help will be appreciated. Thank you.