Use of the "final" keyword in current (merlin) serialization code is
somewhat arbitrary--many private or package-private nested classes are declared
final though they need not be (in these cases, "final" was originally added
under the mistaken impression that it could help performance); many fields
which hold immutable state are not declared final even though they should be.
Declaring as final those fields which store "final" state would make the code
easier to maintain.