Merge pull request faif#205 from jefffffrey/master

fix a minor bug

Author: faif

structural/flyweight.py

@@ -37,7 +37,7 @@ def __call__(cls, *args, **kwargs):
         pool = getattr(cls, 'pool', {})
 
         instance = pool.get(key)
-        if not instance:
+        if instance is None:
             instance = super(FlyweightMeta, cls).__call__(*args, **kwargs)
             pool[key] = instance
         return instance