getChildren method Null safety
override
    Children of this DiagnosticsNode.
See also:
- getProperties, which returns the properties of the DiagnosticsNodeobject.
Implementation
@override
List<DiagnosticsNode> getChildren() {
  if (expandableValue) {
    final T? object = value;
    if (object is DiagnosticsNode) {
      return object.getChildren();
    }
    if (object is Diagnosticable) {
      return object.toDiagnosticsNode(style: style).getChildren();
    }
  }
  return const <DiagnosticsNode>[];
}