import Sequence from "./Sequence";
export declare class SingleOrNull {
    /**
     * Returns the single element of the sequence or `null` if the sequence has more than
     * one element or none at all. If a `predicate` is passed returns the single element matching
     * the predicate or `null` if more or less than one element match the predicate.
     *
     * @param {(value: T) => boolean} predicate
     * @returns {T}
     */
    singleOrNull<T>(this: Sequence<T>, predicate?: (value: T) => boolean): T | null;
}