Fixed bug #189542 by prepending the module to an undefined name.

NEWS.txt

@@ -4,6 +4,8 @@ Whats new in ZODB 3.8.1
 
 Bugs Fixed:
 
+- (beta 9) Fixed bug #189542 by prepending the module for a missing name.
+
 - (beta 8) If there is a failure while FileStorage is finalizing a transaction,
   the file storage is closed because it's internal meta data may be
   invalid.

src/ZEO/ClientStorage.py

@@ -985,7 +985,7 @@ class ClientStorage(object):
             if self._have_blob(blob_filename, oid, serial):
                 return blob_filename
 
-            raise POSKeyError("No blob file", oid, serial)
+            raise POSException.POSKeyError("No blob file", oid, serial)
 
         finally:
             lock.close()