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() < 2 || request.params.size() > 4) {
        std::string msg =
            RPCHelpMan{"addmultisigaddress",
                "\nAdd a nrequired-to-sign multisignature address to the wallet. Requires a new wallet backup.\n"
                "Each key is a Bitcoin address or hex-encoded public key.\n"
                "This functionality is only intended for use with non-watchonly addresses.\n"
                "See `importaddress` for watchonly p2sh address support.\n"
                "If 'label' is specified, assign address to that label.\n",
                {
                    {"nrequired", RPCArg::Type::NUM, RPCArg::Optional::NO, "The number of required signatures out of the n keys or addresses."},
                    {"keys", RPCArg::Type::ARR, RPCArg::Optional::NO, "A json array of bitcoin addresses or hex-encoded public keys",
                        {
                            {"key", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "bitcoin address or hex-encoded public key"},
                        },
                        },
                    {"label", RPCArg::Type::STR, RPCArg::Optional::OMITTED_NAMED_ARG, "A label to assign the addresses to."},
                    {"address_type", RPCArg::Type::STR,  "set by -addresstype", "The address type to use. Options are \"legacy\", \"p2sh-segwit\", and \"bech32\"."},
                },
                RPCResult{
            "{\n"
            "  \"address\":\"multisigaddress\",    (string) The value of the new multisig address.\n"
            "  \"redeemScript\":\"script\"         (string) The string value of the hex-encoded redemption script.\n"