docs: CmsFlexCacheEntry get(CmsFlexRequestKey key) {
  
          if (!isEnabled()) {
              // cache is disabled
              return null;
          }
          Object o = m_keyCache.get(key.getResource());
          if (o != null) {
              // found a matching key in the cache
              CmsFlexCacheVariation v = (CmsFlexCacheVariation)o;
              String variation = v.m_key.matchRequestKey(key);
  
              if (CmsStringUtil.isEmpty(variation)) {
                  // requested resource is not cacheable
                  return null;
              }
              CmsFlexCacheEntry entry = (CmsFlexCacheEntry)v.m_map.get(variation);
              if (entry == null) {
                  // no cache entry available for variation
                  return null;
              }
              if (entry.getDateExpires() < System.currentTimeMillis()) {
                  // cache entry avaiable but expired, remove entry
                  m_variationCache.remove(entry);
                  return null;
              }
              // return the found cache entry
              return entry;
          } else {
              return null;
          }
      }