import { Observable } from "rxjs";
/**
 * If the underlying request throws with a 404 error, it will swallow the error
 * and complete the observable instead. All other errors will be rethrown.
 *
 * You can then set a fallback value with `defaultIfEmpty`.
 *
 * @returns stream which will map 404 errors to `undefined`
 * @example
 * this.http.get<User>('/users/123').pipe(
 *   ignoreNotFound()
 * )
 */
export declare function ignoreNotFound<T>(): (source: Observable<T>) => Observable<T>;