Create a wallet as follows:

```sh
$ bitcoin-cli createwallet "watchonly" true
$ bitcoin-cli -rpcwallet=watchonly getwalletinfo
{
   ...
   "private_keys_enabled": false
}
```

The following should fail, but doesn't:

```sh
$ bitcoin-cli -rpcwallet=watchonly encryptwallet 1234
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.
```

It partially fails silently, because it doesn't actually add a seed. But it does ask for a password when calling `dumpwallet`, which doesn't make sense because we currently don't encrypt anything other than private keys.  
},
            }.ToString());
    }
    auto locked_chain = pwallet->chain().lock();
    LOCK(pwallet->cs_wallet);
    if (!pwallet->IsCrypted()) {
        throw JSONRPCError(RPC_WALLET_WRONG_ENC_STATE, "Error: running with an unencrypted wallet, but walletpassphrase was called.");
    }
    
    SecureString strWalletPass;
    strWalletPass.reserve(100);
    
    
    strWalletPass = request.params[0].get_str().c_str();
    
    int64_t nSleepTime = request.params[1].get_int64();
    
    if (nSleepTime < 0) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Timeout cannot be negative.");
    }
    
    constexpr int64_t MAX_SLEEP_TIME = 100000000; 
    if (nSleepTime > MAX_SLEEP_TIME) {
        nSleepTime = MAX_SLEEP_TIME;
    }
    if (strWalletPass.empty()) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, "passphrase can not be empty");
    }
    if (!pwallet->Unlock(strWalletPass)) {
        throw JSONRPCError(RPC_WALLET_PASSPHRASE_INCORRECT, "Error: The wallet passphrase entered was incorrect.");