parseDateTime function
Parse a date-time string into a DateTime object.
The function attempts to parse the dateString into a DateTime object
using two different date formats: RFC 822 and ISO 8601.
If the dateString is null or cannot be parsed into a DateTime object,
the function returns null.
Implementation
DateTime? parseDateTime(dateString) {
if (dateString == null) return null;
return _parseRfc822DateTime(dateString) ?? _parseIso8601DateTime(dateString);
}