Fix handle_all_serials for the new and old protocols.

src/ZODB/tests/StorageTestBase.py

@@ -113,15 +113,21 @@ def handle_all_serials(oid, *args):
 
     The original interface just returned the serialno for the
     object.
+
+    The updated multi-commit API returns nothing from store(), and
+    returns a sequence of resolved oids from tpc_vote.
     """
     d = {}
     for arg in args:
         if isinstance(arg, bytes):
             d[oid] = arg
-        elif arg is None:
+        elif arg:
+            for t in arg:
+                if isinstance(t, bytes):
+                    # This will be the tid returned by tpc_finish.
                     pass
                 else:
-            for oid, serial in arg:
+                    oid, serial = t
                     if not isinstance(serial, bytes):
                         raise serial # error from ZEO server
                     d[oid] = serial