DevOps, CI/CD and Automation

I have used JAXB to marshall a java class for a date information. The resulting XML data looks fine. It contains the date I want. However, once I'm trying to unmarshall the XML file using JAXB I cannot retrieve the date back.

For example, my object contain a startTime field that is java.util.Calendar.

if I'm doing..... object.getStartTime() I would get null in return?

Does anyone encounter this problem before? Or anyone know a solution to this? Any pointer would be highly appreciated.