code: public final DeterministicKeyChain getActiveKeyChain() {
          checkState(isSupportsDeterministicChains(), "doesn't support deterministic chains");
          if (chains.isEmpty())
              throw new DeterministicUpgradeRequiredException();
          return chains.get(chains.size() - 1);
      }
docs: Returns the key chain that's used for generation of default fresh/current keys. This is always the newest
  deterministic chain. If no deterministic chain is present but imported keys instead, a deterministic upgrate is
  tried.