the package.json patch doesn't recover in the new package

Thanks for your work.

Here I faced two problems.

1. npx patch-package --exclude '^$' doesn't work for me. Something I got was:
----------------------------------------------------------------------------------------------
patch-package 6.2.2
• Creating temporary folder
• Installing ts-loader@5.4.5 with npm
• Diffing your files with clean files
⁉️ Not creating patch file for package 'ts-loader'
⁉️ There don't appear to be any changes.
---------------------------------------------------------------------------------------------

2. So I tried to exclude some non-existent file，e.g. npx patch-package --exclude 'a.txt'. It got worked(I can see the updated package.json in the patch file)
Then, I tried to delete the old package, and do npm install, the package doesn't contain the patch file content.
Btw, the script in my root project package.json, I added
{"postinstall": "patch-package"}

Is there anything I missed? Please feel free to reproduce this issue with any npm package.