On Mon, 12 Sep 2016, Glenn Morris wrote:

> Tino Calancha wrote:
>
>>    "Executable used to create thumbnail.
>> +If nil, `image-dired-create-thumb' signals an error.
>
> I think you could just say:
>
>  "Executable used to create thumbnail, or nil if not found."
That part was reverted after a suggestion from Clément in:
https://lists.gnu.org/archive/html/emacs-devel/2016-09/msg00144.html
I kept those definitions as the original, i.e., just strings, no call
to `executable-find' there.  The check for existing executables is
performed in a new function image-dired--check-executable-exists
which is called on each function using an external program.

> Otherwise, LGTM, thanks.
Thank you very much.
Pushed to master as commit 5d7433ab