Default pull request "merge to" branch to parent branch of "from" branch

When I create a pull request the "to" branch is always set to "master". Most of the time this is what I want, but sometimes I've created a feature branch from a release branch. In this case I want to merge back into this branch, not into master.

I often forget to change the "to" branch (since 95% of the time it's correct) and merge the PR into the wrong branch. This wastes quite a bit of time as I cannot just merge master into the release branch - I have to basically re-do the PR.

Please make the "to" branch default smarter - set it to the parent branch of the "from" branch [see https://stackoverflow.com/questions/3161204/find-the-parent-branch-of-a-git-branch]. If the parent branch cannot be detected then leave the "to" branch blank so that the user must set it manually.