src/vs/workbench/contrib/notebook/common/notebookEditorInput.ts/NotebookEditorInput/save
class NotebookEditorInput:	override async save(group: GroupIdentifier, options?: ISaveOptions): Promise<EditorInput | IUntypedEditorInput | undefined> {
		if (this._editorModelReference) {

			if (this.hasCapability(EditorInputCapabilities.Untitled)) {
				return this.saveAs(group, options);
			} else {
				await this._editorModelReference.object.save(options);
			}

			return this;
		}

		return undefined;
	}