[Bug-ddrescue] Contents of the "bad" sectors in an image file

[Bob Bib]

Hello!

Many thanks to the developers for this useful tool.
Anyway, I have a question.

I've made an image of a faulty drive with the help from dderescue.
The status of the resulting mapfile is "finished",
but still there are few dozens of bad sectors remaining.
The resulting image "outfile" is an ordinary file on an ext4 FS.

Can I expect that all the "bad" blocks in the image file
contain only zeroes,
or should I perform a "fill" pass just to make sure?

Unfortunately, in documentation, I haven't found an explicit indication
of the outfile contents in the case of bad blocks.

--
Best wishes,
Bob