public Cache<Serializable, Session> getActiveSessionsCache() {
        return this.activeSessions;
    }
Returns the cache instance to use for storing active sessions.  If one is not available (it is {@code null}),
it will be {@link CacheManager#getCache(String) acquired} from the {@link #setCacheManager configured}
{@code CacheManager} using the {@link #getActiveSessionsCacheName() activeSessionsCacheName}.

@return the cache instance to use for storing active sessions or {@code null} if the {@code Cache} instance
should be retrieved from the
core/src/main/java/org/apache/shiro/session/mgt/eis/CachingSessionDAO.java