code: private static final String[] deduplicateKeys(String[] keys) {
          synchronized (KEY_CACHE) {
              KEY_HULL.setKeys(keys);
              KeyContainer retrieved = KEY_CACHE.get(KEY_HULL);
              if (retrieved==null) {
                  retrieved = new KeyContainer(keys);
                  KEY_CACHE.put(retrieved, retrieved);
              }
              return retrieved.getKeys();
          }
      }
docs: Deduplicates keys arrays to keep the memory footprint on CompactMap to a minimum.
  
  This implementation is blocking for simplicity. To improve performance in multi-threaded
  environments, use a thread-local KEY_HULL and a concurrent hash map for KEY_CACHE.
  
  @param keys String array to deduplicate by checking against KEY_CACHE
  @return A deduplicated version of the given keys array