client fetch errors when remote repo is empty

client.fetch

from dulwich.client import get_transport_and_path
from dulwich.repo import Repo

# some local repo
local = Repo('/tmp/local')

# /tmp/remote.git is an empty bare repo
client, remote_path = get_transport_and_path('milki@localhost:/tmp/remote.git')
                                                                              
remote_refs = client.fetch(remote_path, local)

####### output #######

Traceback (most recent call last):
  File "client.py", line 12, in <module>
    remote_refs = client.fetch(remote_path, local)
  File "/usr/home/milki/git/dulwich/dulwich/client.py", line 204, in fetch
    target.get_graph_walker(), f.write, progress)
  File "/usr/home/milki/git/dulwich/dulwich/client.py", line 471, in fetch_pack
    refs, server_capabilities = self._read_refs(proto)
  File "/usr/home/milki/git/dulwich/dulwich/client.py", line 172, in _read_refs
    return refs, set(server_capabilities)
TypeError: 'NoneType' object is not iterable
milki@cibo:~/git/dulwich$ fatal: The remote end hung up unexpectedly

client.fetch_pack

from dulwich.client import get_transport_and_path
from dulwich.repo import Repo
from cStringIO import StringIO                                                  

def determine_wants(refs):                                                      
    return refs.values()

# some local repo                                                                                                               local = Repo('/tmp/local')
f = StringIO()    
                                                                    
# /tmp/remote.git is an empty bare repo        
client, remote_path = get_transport_and_path('milki@localhost:/tmp/remote.git')                                                                                 
remote_refs = client.fetch_pack(remote_path, determine_wants, local.get_graph_walker(), f.write)

####### output #######

Traceback (most recent call last):
  File "client.py", line 23, in <module>
    remote_refs = client.fetch_pack(remote_path, determine_wants, local.get_graph_walker(), f.write)
  File "/usr/home/milki/git/dulwich/dulwich/client.py", line 471, in fetch_pack
    refs, server_capabilities = self._read_refs(proto)
  File "/usr/home/milki/git/dulwich/dulwich/client.py", line 172, in _read_refs
    return refs, set(server_capabilities)
TypeError: 'NoneType' object is not iterable
milki@cibo:~/git/dulwich$ fatal: The remote end hung up unexpectedly