/**
 * Calculates the sum of all non-null numbers in an array.
 * @param data - An array of numbers that may include null values
 * @returns The sum of all non-null numbers in the array. Returns 0 for empty arrays or arrays containing only null values.
 * @example
 * sum([1, 2, null, 3]) // Returns 6
 * sum([]) // Returns 0
 * sum([null, null]) // Returns 0
 */
export declare function sum(data: (number | null)[]): number;