Setting _p_changed of a Blob with no uncomitted changes causes error

[Patrick Strawderman]

The following reproduces this issue:

blob = ZODB.blob.Blob('blah')
conn.add(blob)
transaction.commit()
blob._p_changed = True
transaction.commit() # raises an error because blob._uncommitted() is None.

Connection is passing the result of blob._uncommitted() to ClientStorage.storeBlob, which expects a path,
but gets None instead. A TypeError is eventually raised in ZODB.blob.rename_or_copy_blob.
I'm not sure what the correct behavior is here, but this case should probably handled.

[Jim Fulton (jim-zope)]

I'm inclined to consider the correct behavior undefined.

Why do you think someone would set _p_changed on a blob?

[Jim Fulton (jim-zope)]

Never mind, I decided to treat the _p_changed as a noop in this situation.

[Jim Fulton (jim-zope)]

for 3.10b7