code: def get_reference_repository(self, reference: Optional[Path], repo: str) -> Optional[Path]:
          
          if reference is not None:
              return reference.absolute()
  
          repo_path = self.get_path_to_repo(repo)
  
          if not repo_path.exists():
              return None
  
          master = repo_path / "master"
  
          if master.exists() and master.is_dir():
              return master
  
          for existing_branch in repo_path.iterdir():
              if not existing_branch.is_dir():
                  continue
  
              return existing_branch.resolve()
  
          return None
docs: Returns a repository to use in clone command, if there is one to be referenced.
          Either provided by the user of generated from already cloned branches (master is preferred).
  
          :param reference: Path to a local repository provided by the user or None.
          :param repo: Reference for which remote repository.