The argument logger is required.

Signed-off-by: Lucas Carvalho <lucas@nexedi.com>

src/zc/buildout/networkcache.py

@@ -173,7 +173,7 @@ def _get_filename_from_url(url):
            'URL %r produced no filename' % url)
     return name
 
-def fetch_from_network_cache(network_cache, location, tmp, logger=None):
+def fetch_from_network_cache(network_cache, location, tmp, logger):
     """ Try to download from a network cache and preserve
         original filename.
     """