EhCache event listener for preventing caching of null values in data store

ehcache.xml

<cache name="myNonNullCache" 
       <!-- cache configuration --> 
  >
  <cacheEventListenerFactory class="com.example.cache.NotNullCacheEventListenerFactory" />
</cache>

NotNullCacheEventListener.java

package com.example.cache;

import net.sf.ehcache.CacheException;
import net.sf.ehcache.Ehcache;
import net.sf.ehcache.Element;
import net.sf.ehcache.event.CacheEventListener;

final class NotNullCacheEventListener implements CacheEventListener {

	public static final CacheEventListener INSTANCE = new NotNullCacheEventListener();

	@Override
	public void notifyElementRemoved(final Ehcache cache, final Element element) throws CacheException {
	}

	@Override
	public void notifyElementPut(final Ehcache cache, final Element element) throws CacheException {
		removeIfNull(cache, element);
	}

	@Override
	public void notifyElementUpdated(final Ehcache cache, final Element element) throws CacheException {
		removeIfNull(cache, element);
	}

	private void removeIfNull(final Ehcache cache, final Element element) {
		if (element.getObjectValue() == null) {
			cache.remove(element.getKey());
		}
	}

	@Override
	public void notifyElementExpired(final Ehcache cache, final Element element) {
	}

	@Override
	public void notifyElementEvicted(final Ehcache cache, final Element element) {
	}

	@Override
	public void notifyRemoveAll(final Ehcache cache) {
	}

	@Override
	public void dispose() {
	}

	@Override
	public Object clone() throws CloneNotSupportedException {
		throw new CloneNotSupportedException("Singleton instance");
	}
}

NotNullCacheEventListenerFactory .java

package com.example.cache;

import java.util.Properties;

import net.sf.ehcache.event.CacheEventListener;
import net.sf.ehcache.event.CacheEventListenerFactory;

public class NotNullCacheEventListenerFactory extends CacheEventListenerFactory {

	@Override
	public CacheEventListener createCacheEventListener(final Properties properties) {
		return NotNullCacheEventListener.INSTANCE;
	}
}