The caller can't deal with using current data from loadBefore, so hav…

…ing an "end_tid" of None is useless.

TemporaryStorage.py

@@ -153,7 +153,7 @@ def loadBefore(self, oid, tid):
             start_tid = tids[i]
             j = i + 1
             if j == len(tids):
-                end_tid = None
+                return None # the caller can't deal with current data
             else:
                 end_tid = tids[j]
             data = self.loadSerial(oid, start_tid)