Initial scan of branches in a multi-branch-project fails with a null pointer exception. It seems to be due to the addition of GitSCMSource: support custom remote and refspec.

Steps to duplicate the problem:

1. Clone, build, and run the docker instance

     $ git lfs clone https://github.com/MarkEWaite/docker-lfs JENKINS-42204
     $ cd JENKINS-42204
     $ git lfs fetch origin 4bd3aba9910323f8bc279ad5bd7ac3ae8d5ffd5f
     $ git checkout -b lts-with-plugins 4bd3aba9910323f8bc279ad5bd7ac3ae8d5ffd5f
     $ docker build -t jenkins:JENKINS-42204 .
     $ docker run -i --rm --publish 8080:8080 jenkins:JENKINS-42204
   

2. Connect a web browser to that docker instance (http://localhost:8080)
3. Open the "Bugs - Pipeline Checks"
4. Open the "jenkins-bugs" multi-branch pipeline job
5. Click the "Scan Multibranch Pipeline" link and then the "Run Now" link to start branch indexing
6. Click the "Log" link to view the log - stack trace will appear in that log

If I revert the commit for GitSCMSource: support custom remote and refspec, the problem no longer appears. Refer to PR466 for more details.