Summary:
After successfully connecting to a repo on a Bitbucket server which has code, but does not have a Jenkinsfile in it, attempting to create one fails in Blue Ocean. The only error message shown is the word "Found" in red text. This is caused by setting up the Bitbucket server with an HTTP URL, rather than an HTTPS URL. Changing from HTTP to HTTPS resolves the issue.

Routing:
It's unclear to me at the moment if this is an issue in bitbucket-branch-source, in BO itself, in the editor, or somewhere else.

Steps to recreate:
1. Make a local clone of the simple-maven-project-with-tests repo found here.

2. On your Bitbucket server, create a repository, which you'll use as a remote for this repo you just cloned:

3. Using Blue Ocean, connect to this Bitbucket server by providing your credentials. Shown below, I've gotten as far as having found the repo, but have not yet selected it:

4. Click "Create Pipeline." You'll be told there are no Jenkinsfiles, which is expected.

5. Click the second "Create Pipeline" button which was just generated, and you'll be taken to the editor:

6. Leave Agent set to any (the default), and click the button to create a stage. Add a Shell Script step, and enter mvn -X clean package as the step:

7. Click Save, enter a commit message, and leave the default setting of Commit to master. Click Save and Run, and notice the Error at the top of this same dialog:

8. This can also be recreated by using a different branch name than master.

Why this is a problem:

• I've been given no direction as far as what has gone wrong.
• There's nothing at all in the Jenkins log

Later this evening, I'll capture a HAR file while retracing my steps.