extensions/ipynb/src/notebookSerializer.ts/getNotebookMetadata
export function getNotebookMetadata(document: vscode.NotebookDocument | vscode.NotebookData) {
	const notebookContent: Partial<nbformat.INotebookContent> = document.metadata?.custom || {};
	notebookContent.cells = notebookContent.cells || [];
	notebookContent.nbformat = notebookContent.nbformat || 4;
	notebookContent.nbformat_minor = notebookContent.nbformat_minor ?? 2;
	notebookContent.metadata = notebookContent.metadata || { orig_nbformat: 4 };
	return notebookContent;
}