I'd forgotten about removing the version argument in MVCCAdapterInstance

Which led to me to call site that needed it to be removed.

src/ZODB/ExportImport.py

@@ -48,7 +48,7 @@ class ExportImport:
                 continue
             done_oids[oid] = True
             try:
-                p, serial = load(oid, '')
+                p, serial = load(oid)
             except:
                 logger.debug("broken reference for oid %s", repr(oid),
                              exc_info=True)

src/ZODB/mvccadapter.py

@@ -139,7 +139,7 @@ class MVCCAdapterInstance(Base):
                 self._invalidations.clear()
                 return result
 
-    def load(self, oid, version=''):
+    def load(self, oid):
         assert self._start is not None
         r = self._storage.loadBefore(oid, self._start)
         if r is None: