[MERGE] deprecated EmptyTree

[Aaron Bentley]

Robert Collins wrote:
> On Fri, 2006-07-21 at 00:48 -0400, Aaron Bentley wrote:

>> In nested-trees, the empty tree has no root file-id.  The root id is
>> introduced by the first commit.  It must be introduced in the first
>> commit, because the inventory serializer throws an exception if there's
>> no root id.
> 
> Can it still serialize existing trees?

Yes.  I didn't modify the serializer; it already had that constraint.

> Or does their ROOT_ID id count as
> a root file-id ?

Exactly.  TREE_ROOT counts as a root file-id.

Aaron