src/vs/workbench/api/common/extHostTypes.ts/NotebookCellData/validate
class NotebookCellData:	static validate(data: NotebookCellData): void {
		if (typeof data.kind !== 'number') {
			throw new Error('NotebookCellData MUST have \'kind\' property');
		}
		if (typeof data.value !== 'string') {
			throw new Error('NotebookCellData MUST have \'value\' property');
		}
		if (typeof data.languageId !== 'string') {
			throw new Error('NotebookCellData MUST have \'languageId\' property');
		}
	}