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() > 1)
        throw std::runtime_error(
            RPCHelpMan{"listlabels",
                "\nReturns the list of all labels, or labels that are assigned to addresses with a specific purpose.\n",
                {
                    {"purpose", RPCArg::Type::STR, RPCArg::Optional::OMITTED_NAMED_ARG, "Address purpose to list labels for ('send','receive'). An empty string is the same as not providing this argument."},
                },
                RPCResult{
            "[               (json array of string)\n"
            "  \"label\",      (string) Label name\n"
            "  ...\n"
            "]\n"
                },
                RPCExamples{
            "\nList all labels\n"
            + HelpExampleCli("listlabels", "") +
            "\nList labels that have receiving addresses\n"
            + HelpExampleCli("listlabels", "receive") +