Use VoidCallback

lib/hooks/debounce.dart

@@ -7,7 +7,7 @@ import 'ref.dart';
 
 class Debounce {
   final bool loading;
-  final void Function() callback;
+  final VoidCallback callback;
 
   const Debounce({
     @required this.loading,
@@ -20,7 +20,7 @@ class Debounce {
 /// will run `callback()` after debounce hook hasn't been called for the
 /// specified `delayDuration`
 Debounce useDebounce(
-  Future<Null> Function() callback, [
+  Future<void> Function() callback, [
   Duration delayDuration = const Duration(seconds: 1),
 ]) {
   final loading = useState(false);

lib/hooks/delayed_loading.dart

@@ -8,8 +8,8 @@ import 'ref.dart';
 class DelayedLoading {
   final bool pending;
   final bool loading;
-  final void Function() start;
-  final void Function() cancel;
+  final VoidCallback start;
+  final VoidCallback cancel;
 
   const DelayedLoading({
     @required this.pending,

lib/hooks/logged_in_action.dart

@@ -11,14 +11,15 @@ import 'stores.dart';
 /// Snackbar is rendered. If [any] is set to true, this check is performed for
 /// all instances and if any of them have an account, the wrapped action will be
 /// called with a null token.
-Function(
-  Function(Jwt token) action, [
+
+VoidCallback Function(
+  void Function(Jwt token) action, [
   String message,
 ]) useLoggedInAction(String instanceHost, {bool any = false}) {
   final context = useContext();
   final store = useAccountsStore();
 
-  return (Function(Jwt token) action, [message]) {
+  return (action, [message]) {
     if (any && store.hasNoAccount ||
         !any && store.isAnonymousFor(instanceHost)) {
       return () {

lib/widgets/comment.dart

@@ -456,7 +456,7 @@ class _CommentTag extends StatelessWidget {
 
 class _CommentAction extends StatelessWidget {
   final IconData icon;
-  final void Function() onPressed;
+  final VoidCallback onPressed;
   final String tooltip;
   final bool loading;
   final Color iconColor;

lib/widgets/infinite_scroll.dart

@@ -4,7 +4,7 @@ import 'package:flutter_hooks/flutter_hooks.dart';
 import '../hooks/ref.dart';
 
 class InfiniteScrollController {
-  Function() clear;
+  VoidCallback clear;
 
   InfiniteScrollController() {
     usedBeforeCreation() => throw Exception(