Use the default no-command-line-args form of git diff?

[shunf4]

From https://git-scm.com/docs/git-diff :

git diff [<options>] [--] [<path>…​]

This form is to view the changes you made relative to the index (staging area for the next commit). In other words, the differences are what you could tell Git to further add to the index but you still haven’t. You can stage these changes by using git-add[1].

And I do mean to view the changes I made relative to the index. But both diff2html and diff2html -- invoke git diff -M -C HEAD, which is not what I desire. Is there any way to use the default no-command-line-args form of git diff, without exporting the diff to a file and load it in diff2html by -i file?