pack()'s 'wait' argument is a boolean, not an object, so test it using

"if wait" rather than "if wait is not None".  Also change the default
to 0.

src/ZEO/StorageServer.py

@@ -249,8 +249,8 @@ class ZEOStorage:
     def endZeoVerify(self):
         self.client.endVerify()
 
-    def pack(self, time, wait=None):
-        if wait is not None:
+    def pack(self, time, wait=0):
+        if wait:
             return run_in_thread(self.pack_impl, time)
         else:
             # If the client isn't waiting for a reply, start a thread