RedisStorage.get_node_data: return empty result as None

ffstatus/redisstorage.py

@@ -64,7 +64,7 @@ class RedisStorage(BaseStorage):
     def get_node_data(self, key):
         node = {}
         thedata = self.db.hgetall('node_' + key)
-        if thedata is None:
+        if thedata is None or len(thedata) == 0:
             return None
 
         for item in thedata: