values smaller than 0.001 sat/B can't be represented by CFeeRate, but they are not rejected.

```
./src/bitcoin-cli -named sendtoaddress address=bcrt1qwkmhqum095zau5rf2velq55cq938vrd7uw8m4r amount=1.23 fee_rate=0.0009

error code: -6
error message:
Fee rate (0.000 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)
```

```
./src/bitcoin-cli -named sendtoaddress address=bcrt1qwkmhqum095zau5rf2velq55cq938vrd7uw8m4r amount=1.23 fee_rate=0.000000000009

error code: -3
error message:
Invalid amount

}
        if (options.exists("change_type")) {
            if (options.exists("changeAddress") || options.exists("change_address")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both change address and address type options");
            }
            OutputType out_type;
            if (!ParseOutputType(options["change_type"].get_str(), out_type)) {
                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown change type '%s'", options["change_type"].get_str()));
            }
            coinControl.m_change_type.emplace(out_type);
        }
        const UniValue include_watching_option = options.exists("include_watching") ? options["include_watching"] : options["includeWatching"];
        coinControl.fAllowWatchOnly = ParseIncludeWatchonly(include_watching_option, wallet);
        if (options.exists("lockUnspents") || options.exists("lock_unspents")) {
            lockUnspents = (options.exists("lock_unspents") ? options["lock_unspents"] : options["lockUnspents"]).get_bool();
        }
        if (options.exists("feeRate")) {
            if (options.exists("fee_rate")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both fee_rate (" + CURRENCY_ATOM + "/vB) and feeRate (" + CURRENCY_UNIT + "/kvB)");
            }
            if (options.exists("conf_target")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both conf_target and feeRate. Please provide either a confirmation target in blocks for automatic fee estimation, or an explicit fee rate.");
            }
            if (options.exists("estimate_mode")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both estimate_mode and feeRate");
            }
            coinControl.m_feerate = CFeeRate(AmountFromValue(options["feeRate"]));
            coinControl.fOverrideFeeRate = true;
        }
        if (options.exists("subtractFeeFromOutputs") || options.exists("subtract_fee_from_outputs") )