[flutter]: fix bugs

app_flowy/lib/workspace/application/doc/doc_bloc.dart

@@ -58,7 +58,10 @@ class DocBloc extends Bloc<DocEvent, DocState> {
   Future<void> close() async {
     await listener.stop();
 
-    await _subscription?.cancel();
+    if (_subscription != null) {
+      await _subscription?.cancel();
+    }
+
     docManager.closeDoc();
     return super.close();
   }

app_flowy/lib/workspace/presentation/stack_page/doc/widget/toolbar/tool_bar.dart

@@ -71,7 +71,7 @@ class EditorToolbar extends StatelessWidget implements PreferredSizeWidget {
         ),
         FlowyToggleStyleButton(
           attribute: Attribute.italic,
-          normalIcon: 'editor/restore',
+          normalIcon: 'editor/italic',
           iconSize: toolbarIconSize,
           controller: controller,
         ),

rust-lib/flowy-ot/src/core/attributes/attribute.rs

@@ -80,7 +80,7 @@ pub enum AttributeKey {
     Italic,
     #[serde(rename = "underline")]
     Underline,
-    #[serde(rename = "strikethrough")]
+    #[serde(rename = "strike")]
     StrikeThrough,
     #[serde(rename = "font")]
     Font,