# HG changeset patch
# User Patrick Mezard <pmezard@gmail.com>
# Date 1264841370 -3600
# Node ID 7b330c576920ed42eb11daad6cc35e90650ebf87
# Parent  b847e1a3ccd0cc1f70bb5b25e36decea341766c4
svnmeta: speedup get_parent_revision() in common case

diff --git a/hgsubversion/svnmeta.py b/hgsubversion/svnmeta.py
--- a/hgsubversion/svnmeta.py
+++ b/hgsubversion/svnmeta.py
@@ -354,10 +354,11 @@ class SVNMeta(object):
         '''Get the parent revision hash for a commit on a specific branch.
         '''
         tag = self.get_path_tag(self.remotename(branch))
-        limitedtags = maps.TagMap(self.repo, endrev=number-1)
-        if tag in limitedtags:
-            ha = limitedtags[tag]
-            return ha
+        if tag:
+            limitedtags = maps.TagMap(self.repo, endrev=number-1)
+            if tag in limitedtags:
+                ha = limitedtags[tag]
+                return ha
         r, br = self.get_parent_svn_branch_and_rev(number, branch)
         if r is not None:
             return self.revmap[r, br]