@Override
public void serialize(NullValue value, JsonGenerator jgen, SerializerProvider provider)
        throws IOException {

    jgen.writeStartObject();
    jgen.writeStringField(classIdentifier, NullValue.class.getName());
    jgen.writeEndObject();
}
 

@Override
protected Object lookup(Object key) {
    CacheObject cacheObject = cacheChannel.get(j2CacheName, String.valueOf(key));
    if (cacheObject.rawValue() != null && cacheObject.rawValue().getClass().equals(NullObject.class)
        && super.isAllowNullValues()) {
        return NullValue.INSTANCE;
    }
    return cacheObject.getValue();
}
 

@Override
protected Object lookup(Object key) {
	CacheObject cacheObject = cacheChannel.get(j2CacheName, String.valueOf(key), false);
	if(cacheObject.rawValue() != null && cacheObject.rawValue().getClass().equals(NullObject.class) && super.isAllowNullValues()) {
		return NullValue.INSTANCE;
	}
	return cacheObject.getValue();
}
 

@Override
protected Object lookup(Object key) {
    Object value = j2Cache.get(name, getKey(key), false).rawValue();
    if (value == null || value.getClass().equals(Object.class)) {
        return null;
    }
    if (value.getClass().equals(NullObject.class)) {
        return NullValue.INSTANCE;
    }
    return value;
}
 

@Override
protected Object lookup(Object key) {
	CacheObject cacheObject = cacheChannel.get(j2CacheName, String.valueOf(key), false);
	if(cacheObject.rawValue() != null && cacheObject.rawValue().getClass().equals(NullObject.class) && super.isAllowNullValues()) {
		return NullValue.INSTANCE;
	}
	return cacheObject.getValue();
}
 

@Test
public void whenPutNullThenStoreNullValueInstance() {
    when(memcachedClient.get(namespaceKey)).thenReturn(NAMESPACE_KEY_VALUE);

    memcachedCache.put(CACHED_OBJECT_KEY, null);

    verify(memcachedClient).get(namespaceKey);
    verify(memcachedClient).set(memcachedKey, CACHE_EXPIRATION, NullValue.INSTANCE);
    verify(memcachedClient).touch(namespaceKey, CACHE_EXPIRATION);
}
 

/**
 * @param classIdentifier can be {@literal null} and will be defaulted to {@code @class}.
 */
CustomNullValueSerializer(@Nullable String classIdentifier) {

    super(NullValue.class);
    this.classIdentifier = StringUtils.hasText(classIdentifier) ? classIdentifier : "@class";
}
 

NullValueSerializer(@Nullable String classIdentifier) {
    super(NullValue.class);
    this.classIdentifier = StringUtils.hasText(classIdentifier) ? classIdentifier : "@class";
}
 

@Override
public void serialize(NullValue value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
    jgen.writeStartObject();
    jgen.writeStringField(this.classIdentifier, NullValue.class.getName());
    jgen.writeEndObject();
}