in src/main/java/org/apache/jenkins/gitpubsub/ASFGitSCMFileSystem.java [113:121]
public ASFGitSCMFileSystem(String remote, SCMHead head, SCMRevision rev) {
super(rev instanceof AbstractGitSCMSource.SCMRevisionImpl ? rev : null);
this.remote = remote;
this.refOrHash = rev instanceof AbstractGitSCMSource.SCMRevisionImpl
? ((AbstractGitSCMSource.SCMRevisionImpl) rev).getHash()
: (head instanceof GitTagSCMHead
? Constants.R_TAGS + head.getName()
: Constants.R_HEADS + head.getName());
}