Why git format-patch did nothing?

[jimhce]

Hi,

I am running two laptop one is ubuntu 18.04, another is 20.04, I made changes in a git source, the patch files are in patches directors, but when I run git format-patch, it did nothing, it supposed to write cover letter to each patch files, it did not. What I get wrong there?

$ git format-patch --cover-letter origin/master -o patches

It did not write anything to patch files in patches directory.