Every once in awhile we make a mistake. We create a serializable class, usually an exception
class, without an explicit serialVersionUID. An update to the class then changes the implicit
serialVersionUID. It's impossible to create a third version of the class that fixes the bug by
including an explicit serialVersionUID and that handles the serialized data from both of the
previous versions.

It would be nice if the serialization subsystem handled this, e.g, by allowing the class to have an
acceptSerialVersionUID(long uid) method and a long chooseSerialVersionUID() method.
(The reading case is easy; the writing case is harder to know which uid to use.)