serialToDateTime static method
Parses a serial date string (ISO 8601 format) to DateTime.
Args: dateWithT: A date string in ISO 8601 format (e.g., "20231225T120000").
Returns: A DateTime object, or null if the string is null, empty, or invalid.
Implementation
static DateTime? serialToDateTime(String? dateWithT) {
if (dateWithT == null || dateWithT.isEmpty) return null;
return DateTime.tryParse(dateWithT);
}