docs: @Override
      public Subject getSubject(Object cacheKey) {
          Subject subject = null;
          if (cacheKey != null) {
              CacheObject cacheObject = getCachedObject(cacheKey);
              subject = cacheObject != null ? cacheObject.getSubject() : null;
              subject = optionallyRemoveEntryForInvalidSubject(cacheObject, subject);
          }
          return subject;
      }