docs: def clean_doi(doi_string):
      """
      Use regex to extract all DOI ids from string (i.e. 10.1029/2005pa001215)
  
      :param str doi_string: Raw DOI string value from input file. Often not properly formatted.
      :return list: DOI ids. May contain 0, 1, or multiple ids.
      """
      regex = re.compile(r'\b(10[.][0-9]{3,}(?:[.][0-9]+)*/(?:(?!["&\'<>,])\S)+)\b')
      try:
          # Returns a list of matching strings
          m = re.findall(regex, doi_string)
      except TypeError as e:
          # If doi_string is None type, return empty list
          print("TypeError cleaning DOI: {}, {}".format(doi_string, e))
          m = []
      return m