What is default merge strategy for this repository?

[nijkah]

I wonder how open-mmlab manages its repositories in aspect of commit history.
I found that there was no "Merge" commit in the history.

Are all PRs merged with rebase and merge?
Is there any available problem with "rebase and merge" which has the property changes the commit id?

[nijkah]

I think its merge strategy is ' Squash and Merge' because every commits has a PR number.