ObjectUtils.Null

public static class org.apache.commons.lang3.ObjectUtils.Null implements Serializable

Class used as a null placeholder where null has another meaning.

For example, in a HashMap the java.util.HashMap#get(Object) method returns null if the Map contains null or if there is no matching key. The null placeholder can be used to distinguish between these two cases.

Another example is Hashtable, where null cannot be stored.