import type { MaskOptions, MiddlewareField } from './types';
/**
 * Normalizes a middleware `fields` config into a path→options schema.
 * Returns `null` when no fields are configured so callers can fall back
 * to auto-mask strategies without additional branching.
 */
export declare function buildSchemaFromFields(fields: MiddlewareField[] | undefined, globalOptions?: MaskOptions): Record<string, MaskOptions> | null;
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