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.  
{
    std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
    CWallet* const pwallet = wallet.get();
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
    if (request.fHelp || request.params.size() > 0)
        throw std::runtime_error(
            RPCHelpMan{"listlockunspent",
                "\nReturns list of temporarily unspendable outputs.\n"
                "See the lockunspent call to lock and unlock transactions for spending.\n",
                {},
                RPCResult{
            "[\n"
            "  {\n"
            "    \"txid\" : \"transactionid\",     (string) The transaction id locked\n"
            "    \"vout\" : n                      (numeric) The vout value\n"
            "  }\n"
            "  ,...\n"
            "]\n"
                },
                RPCExamples{
            "\nList the unspent transactions\n"
            + HelpExampleCli("listunspent", "") +
            "\nLock an unspent transaction\n"