Hi Danh,

> It seems like only David Aguilar (Cc-ed) works on that file.
>Look into  b12d04503b (mergetools/meld: make usage of `--output` configurable and more robust, 2014-10-15), it looks like we need to check if --auto-merge option is available in meld.
>Someone still live with the ancient tools ;).
>meld has known --output for a long time but we still have a check for it.

Thank you for your hints, I changed the patch for checking the option "--auto-merge" in meld and use this option only if it's available.
The last patch is appended in attachment, or https://github.com/git/git/commit/3b70fd0bfc4086a08e27c869ff7492d567e8fdc2

Look forward it can be merged this time. 
Thanks

Regards
Lin