code: public T get(final long _id)
      {
          return getCache4Id() == null ? null : getCache4Id().get(new Long(_id));
      }
docs: Returns for given key id the cached object from the cache4Id cache. If
  the cache was not initialized yet, <code>null</code> is returned.
  
  @see #getCache4Id()
  @param _id       id of the searched cached object
  @return cached object