toCli method
Implementation
@override
String toCli() {
final argList = <String>[
'type=$type',
if (startTime != null) 'start_time=${startTime!.toSeconds()}',
if (duration != null) 'duration=${duration!.toSeconds()}',
if (curve != null) 'curve=$curve'
];
return 'afade=${argList.join(':')}';
}