fix: remove the unnecessary operation in enter keyhandler

frontend/app_flowy/packages/appflowy_editor/lib/src/service/internal_key_event_handlers/enter_without_shift_in_text_node_handler.dart

@@ -153,11 +153,13 @@ ShortcutEventHandler enterWithoutShiftInTextNodesHandler =
       delta: textNode.delta.slice(selection.end.offset),
     ),
   );
-  transaction.deleteText(
-    textNode,
-    selection.start.offset,
-    textNode.toPlainText().length - selection.start.offset,
-  );
+  if (selection.end.offset != textNode.toPlainText().length) {
+    transaction.deleteText(
+      textNode,
+      selection.start.offset,
+      textNode.toPlainText().length - selection.start.offset,
+    );
+  }
   if (textNode.children.isNotEmpty) {
     final children = textNode.children.toList(growable: false);
     transaction.deleteNodes(children);

frontend/app_flowy/packages/appflowy_editor/lib/src/service/render_plugin_service.dart

@@ -78,10 +78,10 @@ class AppFlowyRenderPlugin extends AppFlowyRenderPluginService {
       node.key = key;
       return _autoUpdateNodeWidget(builder, context);
     } else {
-      assert(false,
-          'Could not query the builder with this $name, or nodeValidator return false.');
-      // TODO: return a placeholder widget with tips.
-      return Container();
+      // Returns a SizeBox with 0 height if no builder found.
+      return const SizedBox(
+        height: 0,
+      );
     }
   }