build method Null safety

Implementation

@override
Widget build(BuildContext context) {
  final Widget tmpTitle;
  if (icon == null) {
    tmpTitle = title;
  } else {
    tmpTitle = Row(
      mainAxisAlignment: isCompactTitle
          ? MainAxisAlignment.start
          : MainAxisAlignment.spaceBetween,
      crossAxisAlignment: CrossAxisAlignment.center,
      children: <Widget>[title, icon!],
    );
  }
  final Widget displayed = Padding(
    padding: const EdgeInsets.symmetric(
      horizontal: LARGE_SPACE,
      vertical: SMALL_SPACE,
    ),
    child: Column(
      mainAxisAlignment: MainAxisAlignment.start,
      crossAxisAlignment: CrossAxisAlignment.start,
      children: <Widget>[
        const SizedBox(height: SMALL_SPACE),
        tmpTitle,
        const SizedBox(height: VERY_SMALL_SPACE),
        if (subtitle != null) subtitle!,
      ],
    ),
  );
  if (onTap == null && onLongPress == null) {
    return displayed;
  }
  return InkWell(
    onTap: onTap,
    onLongPress: onLongPress,
    child: displayed,
  );
}