1export function isNotNull<T>(a: T): boolean {
 2  return a !== null;
 3}
 4
 5export function isNull<T>(a: T): boolean {
 6  return a === null;
 7}
 8
 9export function isNotUndefined<T>(a: T): boolean {
10  return a !== undefined;
11}
12
13export function isUndefined<T>(a: T): boolean {
14  return a === undefined;
15}