[MERGE] Fix PlanMergeVersionedFile's no-parent handling

[Aaron Bentley]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hi all,

This patch fixes _PlanMergeVersionedFile to be consistent with the
VersionedFiles interface.

There seems to be some confusion here;

StackedParentsProvider.get_parent_map is documented to return
NULL_REVISION when queried about a revision with no parent revisions.

But VersionedFiles.get_parent_map returns ().

Furthermore, we have code that expects () for get_parent_map, but we
also have code that expects NULL_REVISION.

Note that NULL_REVISION is not a tuple, so this is a pretty bizarre
return type for methods that are supposed to return keys.

The code I am proposing takes the path of least resistance, by making
PlanMergeVersionedFile conform more closely to the VersionedFiles API.

Aaron
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.6 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFIa7eC0F+nu1YWqI0RAsDpAJ9NM35cAvEDnQbiBN8/Ilui2UqRYQCfShoj
PkmmPLifRYUBT5mt7dh2u9g=
=emjP
-----END PGP SIGNATURE-----
-------------- next part --------------
A non-text attachment was scrubbed...
Name: fix-plan-merge-3519.patch
Type: text/x-diff
Size: 5671 bytes
Desc: not available
Url : https://lists.ubuntu.com/archives/bazaar/attachments/20080702/db1a5dd4/attachment.bin