diff --git a/keep-notes/components/note-editor.tsx b/keep-notes/components/note-editor.tsx
index 056d06c..dcdc2e4 100644
--- a/keep-notes/components/note-editor.tsx
+++ b/keep-notes/components/note-editor.tsx
@@ -1110,7 +1110,7 @@ export function NoteEditor({ note, readOnly = false, onClose }: NoteEditorProps)
               type: 'text',
               isMarkdown: true, // AI generates markdown content
               autoGenerated: true, // Mark as AI-generated fused note
-              notebookId: fusionNotes[0].notebookId // Keep the notebook from the first note
+              notebookId: fusionNotes[0].notebookId ?? undefined // Keep the notebook from the first note, convert null to undefined
             })
 
             // Archive original notes if option is selected