code: @SuppressWarnings("unchecked")
      <HK> byte[] rawHashKey(HK hashKey) {
          Assert.notNull(hashKey, "non null hash key required");
          return hashKeySerializer().serialize(hashKey);
      }
docs: Raw hash key.
  
  @param <HK>    the generic type
  @param hashKey the hash key
  @return the byte[]