code: def get_previous_version(version: str) -> Optional[str]:
      
      debug('get_previous_version')
      found_version = False
      for commit_hash, commit_message in get_commit_log():
          debug('checking commit {}'.format(commit_hash))
          if version in commit_message:
              found_version = True
              debug('found_version in "{}"'.format(commit_message))
              continue
  
          if found_version:
              matches = re.match(r'v?(\d+.\d+.\d+)', commit_message)
              if matches:
                  debug('version matches', commit_message)
                  return matches.group(1).strip()
  
      return get_last_version([version, 'v{}'.format(version)])
docs: Returns the version prior to the given version.
  
      :param version: A string with the version number.
      :return: A string with the previous version number