Fix fetch_object use of determine_wants. Fix repo.get_refs() - there might not be a HEAD.

dulwich/repo.py

@@ -155,7 +155,9 @@ class Repo(object):
         return self._get_ref(file)
 
   def get_refs(self):
-    ret = {"HEAD": self.head()}
+    ret = {}
+    if self.head():
+        ret['HEAD'] = self.head()
     for dir in ["refs/heads", "refs/tags"]:
         for name in os.listdir(os.path.join(self.controldir(), dir)):
           path = os.path.join(self.controldir(), dir, name)

dulwich/server.py

@@ -85,7 +85,7 @@ class GitBackend(Backend):
         print "pack applied"
 
     def fetch_objects(self, determine_wants, graph_waker, progress):
-        for sha in generate_pack_contents(determine_wants(), have, self.repo.get_object):
+        for sha in generate_pack_contents(determine_wants(self.get_refs()), have, self.repo.get_object):
             yield self.repo.get_object(sha)