fix: delete the divider on mobile will raise an error

lib/src/editor/editor_component/service/ime/delta_input_on_delete_impl.dart

@@ -15,18 +15,13 @@ Future<void> onDelete(
 
   // IME
   if (selection.isSingle) {
-    if (deletion.composing.isValid || !deletion.deletedRange.isCollapsed) {
+    final node = editorState.getNodeAtPath(selection.start.path);
+    if (node?.delta != null &&
+        (deletion.composing.isValid || !deletion.deletedRange.isCollapsed)) {
       final node = editorState.getNodesInSelection(selection).first;
       final start = deletion.deletedRange.start;
       final length = deletion.deletedRange.end - start;
-      // final firstNodeContainsDelta = editorState.document.root.children
-      //     .firstWhereOrNull((element) => element.delta != null);
-      // if (firstNodeContainsDelta != null &&
-      //     node.path.equals(firstNodeContainsDelta.path) && start == 0) {
-
-      //     }
       final transaction = editorState.transaction;
-
       transaction.deleteText(node, start, length);
       await editorState.apply(transaction);
       return;

lib/src/editor/editor_component/service/shortcuts/command_shortcut_events/backspace_command.dart

@@ -40,14 +40,29 @@ CommandShortcutEventHandler _backspaceInCollapsedSelection = (editorState) {
 
   final position = selection.start;
   final node = editorState.getNodeAtPath(position.path);
-  if (node == null || node.delta == null) {
+  if (node == null) {
     return KeyEventResult.ignored;
   }
 
+  final transaction = editorState.transaction;
+
+  // delete the entire node if the delta is empty
+  if (node.delta == null) {
+    transaction.deleteNode(node);
+    transaction.afterSelection = Selection.collapsed(
+      Position(
+        path: position.path,
+        offset: 0,
+      ),
+    );
+    editorState.apply(transaction);
+    return KeyEventResult.handled;
+  }
+
   // Why do we use prevRunPosition instead of the position start offset?
   // Because some character's length > 1, for example, emoji.
   final index = node.delta!.prevRunePosition(position.offset);
-  final transaction = editorState.transaction;
+
   if (index < 0) {
     // move this node to it's parent in below case.
     // the node's next is null

lib/src/editor/toolbar/mobile/toolbar_items/divider_mobile_toolbar_item.dart

@@ -15,10 +15,18 @@ final dividerMobileToolbarItem = MobileToolbarItem.action(
       return;
     }
     final insertedPath = delta.isEmpty ? path : path.next;
-    final transaction = editorState.transaction
-      ..insertNode(insertedPath, dividerNode())
-      ..insertNode(insertedPath, paragraphNode())
-      ..afterSelection = Selection.collapsed(Position(path: insertedPath.next));
+    final transaction = editorState.transaction;
+    transaction.insertNode(insertedPath, dividerNode());
+    // only insert a new paragraph node when the next node is not a paragraph node
+    //  and its delta is not empty.
+    final next = node.next;
+    if (next == null ||
+        next.type != ParagraphBlockKeys.type ||
+        next.delta?.isNotEmpty == true) {
+      transaction.insertNode(insertedPath, paragraphNode());
+    }
+    transaction.afterSelection =
+        Selection.collapsed(Position(path: insertedPath.next));
     editorState.apply(transaction);
   }),
 );