When scanning a repository, if the source fork of a pull request have been deleted the scan fails:
ERROR: [Mon Dec 09 22:02:34 GMT 2019] Could not fetch branches from source 09803c5b-0046-46ea-8ed5-3f98d5cf31e7
java.lang.NullPointerException
at org.jenkinsci.plugins.github_branch_source.PullRequestSCMHead.<init>(PullRequestSCMHead.java:95)
at org.jenkinsci.plugins.github_branch_source.GitHubSCMSource.retrievePullRequest(GitHubSCMSource.java:1168)
at org.jenkinsci.plugins.github_branch_source.GitHubSCMSource.retrieve(GitHubSCMSource.java:1027)
at jenkins.scm.api.SCMSource._retrieve(SCMSource.java:373)
at jenkins.scm.api.SCMSource.fetch(SCMSource.java:283)
at jenkins.branch.MultiBranchProject.computeChildren(MultiBranchProject.java:635)
at com.cloudbees.hudson.plugins.folder.computed.ComputedFolder.updateChildren(ComputedFolder.java:277)
at com.cloudbees.hudson.plugins.folder.computed.FolderComputation.run(FolderComputation.java:164)
at jenkins.branch.MultiBranchProject$BranchIndexing.run(MultiBranchProject.java:1026)
at hudson.model.ResourceController.execute(ResourceController.java:97)
at hudson.model.Executor.run(Executor.java:429)
[Mon Dec 09 22:02:34 GMT 2019] Finished branch indexing. Indexing took 7.4 sec