/**
 * Bar object the chart element can plot.
 * Single series: category × metric, no groupBy.
 * Grouped: a second category column, never the same field as the axes.
 * Many categories flip to horizontal so the labels stay readable.
 */
export declare function barChartPayload(_chartType: string | undefined, fields: Record<string, string>, rows: Record<string, unknown>[]): unknown | null;