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());
    }
    WalletRescanReserver reserver(pwallet);
    if (!reserver.reserve()) {
        throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
    }
    int start_height = 0;
    uint256 start_block, stop_block;
    {
        auto locked_chain = pwallet->chain().lock();
        Optional<int> tip_height = locked_chain->getHeight();
        if (!request.params[0].isNull()) {
            start_height = request.params[0].get_int();
            if (start_height < 0 || !tip_height || start_height > *tip_height) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid start_height");
            }
        }
        Optional<int> stop_height;
        if (!request.params[1].isNull()) {
            stop_height = request.params[1].get_int();
            if (*stop_height < 0 || !tip_height || *stop_height > *tip_height) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid stop_height");
            }
            else if (*stop_height < start_height) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "stop_height must be greater than start_height");
            }
        }
        
        if (locked_chain->findPruned(start_height, stop_height)) {
            throw JSONRPCError(RPC_MISC_ERROR, "Can't rescan beyond pruned data. Use RPC call getblockchaininfo to determine your pruned height.");