message: interfaces: Avoid interface instance if wallet is null
diff: @@ -523,7 +523,7 @@ public:
  } // namespace
  -std::unique_ptr<Wallet> MakeWallet(const std::shared_ptr<CWallet>& wallet) { return MakeUnique<WalletImpl>(wallet); }
  +std::unique_ptr<Wallet> MakeWallet(const std::shared_ptr<CWallet>& wallet) { return wallet ? MakeUnique<WalletImpl>(wallet) : nullptr; }
  std::unique_ptr<ChainClient> MakeWalletClient(Chain& chain, std::vector<std::string> wallet_filenames)
  {
  