ConcurrentHashMap - MissingFieldException: No field 'segmentMask' found in class

import java.util.concurrent.ConcurrentHashMap;

import com.thoughtworks.xstream.XStream;

public class ConcurrentHashMapTest {
	public static void main(String[] args) {
		ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<String, Integer>() {
			private static final long serialVersionUID = 1L;
		};
		
		 XStream xstream = new XStream();
		 
		 @SuppressWarnings("unchecked")
		 ConcurrentHashMap<String, Integer> copyOfMap = (ConcurrentHashMap<String, Integer>) xstream.fromXML(xstream.toXML(map));
		
		assert(copyOfMap.equals(map));		
	}
}