ignore line when server returns an EXPIRE_STRING with an empty value.

[jdigilio]

When checking my domains, I found that the whois server was returning these lines: Registry Expiry Date: 2021-02-13T22:31:37Z Registrar Registration Expiration Date:

The second one, with an empty expiration date, would cause it to throw an error: Traceback (most recent call last): File "dns-domain-expiration-checker.py", line 242, in main() File "dns-domain-expiration-checker.py", line 227, in main expiration_date, registrar = make_whois_query(conf_options["domainname"]) File "dns-domain-expiration-checker.py", line 88, in make_whois_query return(parse_whois_data(whois_data)) File "dns-domain-expiration-checker.py", line 101, in parse_whois_data expiration_date = dateutil.parser.parse(line.partition(": ")[2], ignoretz=True) File "/home/joe/local/lib/python2.7/site-packages/dateutil/parser/_parser.py", line 1301, in parse return DEFAULTPARSER.parse(timestr, **kwargs) File "/home/joe/local/lib/python2.7/site-packages/dateutil/parser/_parser.py", line 610, in parse raise ValueError("String does not contain a date:", timestr) ValueError: (u'String does not contain a date:', '')

In this pull request, if the date value is empty it moves on to parsing the next line of the whois data.