code: def _add_apt_repository(spec):
      
      if '{series}' in spec:
          series = get_distrib_codename()
          spec = spec.replace('{series}', series)
      # software-properties package for bionic properly reacts to proxy settings
      # passed as environment variables (See lp:1433761). This is not the case
      # LTS and non-LTS releases below bionic.
      _run_with_retries(['add-apt-repository', '--yes', spec],
                        cmd_env=env_proxy_settings(['https']))
docs: Add the spec using add_apt_repository
  
      :param spec: the parameter to pass to add_apt_repository
      :type spec: str