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

sections.PushSection({indent + maybe_key + "\"str\"" + maybe_separator, Description("string")});
        return;
    }
    case Type::STR_AMOUNT: {
        sections.PushSection({indent + maybe_key + "n" + maybe_separator, Description("numeric")});
        return;
    }
    case Type::STR_HEX: {
        sections.PushSection({indent + maybe_key + "\"hex\"" + maybe_separator, Description("string")});
        return;
    }
    case Type::NUM: {
        sections.PushSection({indent + maybe_key + "n" + maybe_separator, Description("numeric")});
        return;
    }
    case Type::NUM_TIME: {
        sections.PushSection({indent + maybe_key + "xxx" + maybe_separator, Description("numeric")});
        return;
    }
    case Type::BOOL: {
        sections.PushSection({indent + maybe_key + "true|false" + maybe_separator, Description("boolean")});
        return;
    }
    case Type::ARR_FIXED:
    case Type::ARR: {
        sections.PushSection({indent + maybe_key + "[", Description("json array")});
        for (const auto& i : m_inner) {
            i.ToSections(sections, OuterType::ARR, current_indent + 2);
        }
        CHECK_NONFATAL(!m_inner.empty());