chore: Follow up null safety fixes

lib/pages/chat/events/html_message.dart

@@ -76,15 +76,17 @@ class HtmlMessage extends StatelessWidget {
       onImageTap: (String mxc) => showDialog(
           context: Matrix.of(context).navigatorContext,
           useRootNavigator: false,
-          builder: (_) => ImageViewer(Event.fromJson({
-                'type': EventTypes.Message,
-                'content': <String, dynamic>{
-                  'body': mxc,
-                  'url': mxc,
-                  'msgtype': MessageTypes.Image,
-                },
-                'event_id': 'fake_event',
-              }, room))),
+          builder: (_) => ImageViewer(Event(
+              type: EventTypes.Message,
+              content: <String, dynamic>{
+                'body': mxc,
+                'url': mxc,
+                'msgtype': MessageTypes.Image,
+              },
+              senderId: room.client.userID!,
+              originServerTs: DateTime.now(),
+              eventId: 'fake_event',
+              room: room))),
       setCodeLanguage: (String key, String value) async {
         await matrix.store.setItem('${SettingKeys.codeLanguage}.$key', value);
       },

lib/pages/chat/sticker_picker_dialog.dart

@@ -63,14 +63,17 @@ class StickerPickerDialogState extends State<StickerPickerDialog> {
             physics: const NeverScrollableScrollPhysics(),
             itemBuilder: (BuildContext context, int imageIndex) {
               final image = pack.images[imageKeys[imageIndex]]!;
-              final fakeEvent = Event.fromJson(<String, dynamic>{
-                'type': EventTypes.Sticker,
-                'content': <String, dynamic>{
+              final fakeEvent = Event(
+                type: EventTypes.Sticker,
+                content: {
                   'url': image.url.toString(),
                   'info': image.info,
                 },
-                'event_id': 'fake_event',
-              }, widget.room);
+                originServerTs: DateTime.now(),
+                room: widget.room,
+                eventId: 'fake_event',
+                senderId: widget.room.client.userID!,
+              );
               return InkWell(
                 key: ValueKey(image.url.toString()),
                 onTap: () {

lib/pages/settings_emotes/settings_emotes.dart

@@ -33,10 +33,10 @@ class EmotesSettingsController extends State<EmotesSettings> {
     final event = (room != null
             ? room!.getState('im.ponies.room_emotes', stateKey ?? '')
             : client.accountData['im.ponies.user_emotes']) ??
-        BasicEvent.fromJson(<String, dynamic>{
-          'type': 'm.dummy',
-          'content': <String, dynamic>{},
-        });
+        BasicEvent(
+          type: 'm.dummy',
+          content: {},
+        );
     // make sure we work on a *copy* of the event
     return BasicEvent.fromJson(event.toJson()).parsedImagePackContent;
   }