Summary:
It's not possible to create a new Pipeline based on a personal repository on a Bitbucket server. This is because the Pipeline creation wizard starts by having the user select a Bitbucket "Project." But personal repositories aren't part of a project in Bitbucket. This means you'll never be able to build them.

Prerequisites:

• A Bitbucket Server running 5.2.0 or higher

Steps to recreate:
1. Create a personal repo on Bitbucket. To do this, click on your avatar in the top right corner, and select "View Profile"

2. From your profile page, click "Create Repository" as shown here:

3. Go through the standard steps of creating a repository as you normally would. In my example, I've got a super simple repo with a Jenkinsfile and a README:

4. Switch over to Jenkins, launch Blue Ocean, and click the "New Pipeline" button.

5. Select your Bitbucket server (or add it, if it's not already there).

6. Click "Next." Notice that the only way forward is to select a Project, and the private repo you created in steps 2-3 above doesn't live inside of a project. Meaning, there's no way to get Blue Ocean to see it.