oneOrUndefined / singleOrNone

[phiresky]

is missing

[hediet]

Introduced singleOrUndefined:

	public async singleOrUndefined<TRow extends Row>(query: Query<TRow, any>): Promise<MapOutType<TRow> | undefined> {
		if (query instanceof RetrievalQuery)
			query = query.limit(2);
		const rows = await this.exec(query);
		if (rows.length === 0) return undefined;
		if (rows.length >= 2) throw new Error("More than one row returned.");
		return rows[0];
	}