This is the error I get:

```
$ bitcoin-cli -rpcwallet=descriptor -testnet upgradewallet                         <
error code: -1
error message:
wallet/rpcwallet.cpp:4522 (operator())
Internal bug detected: '!error.empty()'
You may report this issue here: https://github.com/bitcoin/bitcoin/issues
```

The daemon logs this:

```
2021-07-15T16:16:54Z [descriptor] Performing wallet upgrade to 169900
```

**Expected behavior**

When I do the same on the default (non-descriptor) wallet:

```
$ bitcoin-cli -rpcwallet="" -testnet upgradewallet                             
{
  "wallet_name": "",
  "previous_version": 169900,
  "current_version": 169900,
  "result": "Already at latest version. Wallet version unchanged."
}
```

<!-- **Actual behavior** -->

<!-- See above. Isn't this kind of backwards, to first ask what I expect and then ask what I got? I am writing here because I got something strange in the first place... -->

**System information**

Bitcoin Core v0.21.1 Linux x86_64 glibc (Ubuntu) using binarias from bitcoincore.org

{
        int nVersion = s.GetVersion();
        if (!(s.GetType() & SER_GETHASH)) {
            s >> nVersion;
        }
        s >> nTime >> vchPubKey;
        try {
            s >> fInternal;
        } catch (std::ios_base::failure&) {
            /* flag as external address if we can't read the internal boolean
               (this will be the case for any wallet before the HD chain split version) */
            fInternal = false;
        }
        try {
            s >> m_pre_split;
        } catch (std::ios_base::failure&) {
            /* flag as postsplit address if we can't read the m_pre_split boolean
               (this will be the case for any wallet that upgrades to HD chain split) */
            m_pre_split = false;
        }
    }
};
class KeyIDHasher