Option to disable deletion of certain branches when merging pull requests

Currently, a branch can' be deleted during a merge of a pull request if:

The branch is the default repository branch.
The user does not have permission to delete the branch.
The branch is subject to an open pull request.

I suggest adding an option do disable deletion of certain branches in a pull request merging in order to prevent accidental deletion of branches by people who have write permission on the branch.