Update lib/src/selection_dialog.dart

Co-authored-by: Chandra Abdul Fattah <chandrashibezzo@gmail.com>

lib/src/selection_dialog.dart

@@ -10,7 +10,7 @@ class SelectionDialog extends StatefulWidget {
   final InputDecoration searchDecoration;
   final TextStyle? searchStyle;
   final TextStyle? textStyle;
-  final TextStyle headerTextStyle;
+  final TextStyle? headerTextStyle;
   final BoxDecoration? boxDecoration;
   final WidgetBuilder? emptySearchBuilder;
   final bool? showFlag;