https://travis-ci.org/github/MarcoFalke/btc_nightly/jobs/680655419#L412
if (pwallet->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
        throw JSONRPCError(RPC_WALLET_ENCRYPTION_FAILED, "Error: wallet does not contain private keys, nothing to encrypt.");
    }
    if (pwallet->IsCrypted()) {
        throw JSONRPCError(RPC_WALLET_WRONG_ENC_STATE, "Error: running with an encrypted wallet, but encryptwallet was called.");
    }
    
    
    SecureString strWalletPass;
    strWalletPass.reserve(100);
    strWalletPass = request.params[0].get_str().c_str();
    if (strWalletPass.empty()) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, "passphrase can not be empty");
    }
    if (!pwallet->EncryptWallet(strWalletPass)) {
        throw JSONRPCError(RPC_WALLET_ENCRYPTION_FAILED, "Error: Failed to encrypt the wallet.");
    }
    return "wallet encrypted; The keypool has been flushed and a new HD seed was generated (if you are using HD). You need to make a new backup.";
}
static UniValue lockunspent(const JSONRPCRequest& request)
{
    std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
    CWallet* const pwallet = wallet.get();
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
            RPCHelpMan{"lockunspent",
                "\nUpdates list of temporarily unspendable outputs.\n"
                "Temporarily lock (unlock=false) or unlock (unlock=true) specified transaction outputs.\n"
                "If no transaction outputs are specified when unlocking then all current locked transaction outputs are unlocked.\n"