Geo server http session listener proxy

"This method may contain an instance of double-checked locking.  This idiom is not correct according to the semantics of the Java memory model.  For more information, see the web page http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html." - findbugs

It seems to me 
protected Set<HttpSessionListener> listeners() 
is used in  public class GeoServerHttpSessionListenerProxy 
only.
And Where do you use the class GeoServerHttpSessionListenerProxy?