http://github.com/FasterXML/jackson: General data-binding functionality for Jackson: works on core streaming API (FasterXML)
  • Tatu Saloranta
  • Christopher Currie
  • Paul Brown 
package com.fasterxml.jackson.databind.annotation;


Marker class used with annotations to indicate "no class". This is
a silly but necessary work-around -- annotations cannot take nulls
as either default or explicit values. Hence for class values we must
explicitly use a bogus placeholder to denote equivalent of
"no class" (for which 'null' is usually the natural choice).

 Note that since 2.4, most (but not all! JsonTypeInfo.defaultImpl is a notable exception}) usage should start using Void instead as the "not defined" marker. 
/**
 * Marker class used with annotations to indicate "no class". This is
 * a silly but necessary work-around -- annotations cannot take nulls
 * as either default or explicit values. Hence for class values we must
 * explicitly use a bogus placeholder to denote equivalent of
 * "no class" (for which 'null' is usually the natural choice).
 *<p>
 * Note that since 2.4, most (but not all!
 * {@link com.fasterxml.jackson.annotation.JsonTypeInfo#defaultImpl} is
 * a notable exception}) usage should start using
 * {@link java.lang.Void} instead as the "not defined" marker.
 */
public final class NoClass
{
    private NoClass() { }
}