/**
 * Calculates the average (mean) of non-null values in an array.
 * @param data - An array of numbers that may include null values
 * @returns The average of all non-null numbers. Returns 0 for empty arrays.
 * @example
 * avg([1, 2, null, 3]) // Returns 2
 * avg([]) // Returns 0
 * avg([null, null]) // Returns 0
 */
export declare function avg(data: (number | null)[]): number;