public interface PdxUnreadFields
readUnreadFields. If you call readUnreadFields then you must
 also call writeUnreadFields when that object
 is reserialized. If you do not call writeUnreadFields but you did call readUnreadFields the
 unread fields will not be written.
 
 Unread fields are those that are not explicitly read with a PdxReader readXXX method.
 This should only happen when a domain class has changed by adding or removing one or more fields.
 Unread fields will be preserved automatically (unless you turn this feature off using
 setPdxIgnoreUnreadFields or
 client
 setPdxIgnoreUnreadFields) but to reduce the performance and memory overhead of automatic
 preservation it is recommended that use readUnreadFields if
 possible.