Merge "The --why parameter in whichgit should be optional"

  # Print the list of git directories that has one or more of the sources in it

  for project in sorted(get_referenced_projects(get_git_dirs(), sources)):

    print(project)

    if args.why:

      if "*" in args.why or project in args.why:

        prefix = project + "/"

        for f in sources: