`ScanForWalletTransactions()` has the following comment about its return value:

```
 * Returns null if scan was successful. Otherwise, if a complete rescan was not
 * possible (due to pruning or corruption), returns pointer to the most recent
 * block that could not be scanned.
```

This is not strictly true. If `abortrescan` is called, then `ScanForWalletTransactions()` will return `nullptr`, even though the scan wasn't successful to the tip.

This in turn causes a minor bug in `importmulti`, where the call doesn't return the correct error and warning about potentially not finding transactions if `abortrescan` was called.

I think the correct fix is for `ScanForWalletTransactions()` to inform the caller that the rescan was aborted.
vecSend.push_back(recipient);
    CTransactionRef tx;
    if (!pwallet->CreateTransaction(locked_chain, vecSend, tx, reservekey, nFeeRequired, nChangePosRet, strError, coin_control)) {
        if (!fSubtractFeeFromAmount && nValue + nFeeRequired > curBalance)
            strError = strprintf("Error: This transaction requires a transaction fee of at least %s", FormatMoney(nFeeRequired));
        throw JSONRPCError(RPC_WALLET_ERROR, strError);
    }
    CValidationState state;
    if (!pwallet->CommitTransaction(tx, std::move(mapValue), {} , reservekey, g_connman.get(), state)) {
        strError = strprintf("Error: The transaction was rejected! Reason given: %s", FormatStateMessage(state));
        throw JSONRPCError(RPC_WALLET_ERROR, strError);
    }
    return tx;
}
static UniValue sendtoaddress(const JSONRPCRequest& request)
{
    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() > 8)
        throw std::runtime_error(
            "sendtoaddress \"address\" amount ( \"comment\" \"comment_to\" subtractfeefromamount replaceable conf_target \"estimate_mode\")\n"
            "\nSend an amount to a given address.\n"
            + HelpRequiringPassphrase(pwallet) +
            "\nArguments:\n"
            "1. \"address\"            (string, required) The bitcoin address to send to.\n"
            "2. \"amount\"             (numeric or string, required) The amount in " + CURRENCY_UNIT + " to send. eg 0.1\n"
            "3. \"comment\"            (string, optional) A comment used to store what the transaction is for. \n"