code: def get_or_guess_paths_to_mutate(paths_to_mutate):
      
      if paths_to_mutate is None:
          # Guess path with code
          this_dir = os.getcwd().split(os.sep)[-1]
          if isdir('lib'):
              return 'lib'
          elif isdir('src'):
              return 'src'
          elif isdir(this_dir):
              return this_dir
          elif isdir(this_dir.replace('-', '_')):
              return this_dir.replace('-', '_')
          elif isdir(this_dir.replace(' ', '_')):
              return this_dir.replace(' ', '_')
          elif isdir(this_dir.replace('-', '')):
              return this_dir.replace('-', '')
          elif isdir(this_dir.replace(' ', '')):
              return this_dir.replace(' ', '')
          else:
              raise FileNotFoundError(
                  'Could not figure out where the code to mutate is. '
                  'Please specify it on the command line using --paths-to-mutate, '
                  'or by adding "paths_to_mutate=code_dir" in setup.cfg to the [mutmut] section.')
      else:
          return paths_to_mutate
docs: :type paths_to_mutate: str or None
      :rtype: str