Function deserialize_optional_decimal_str 

pub fn deserialize_optional_decimal_str<'de, D>(
    deserializer: D,
) -> Result<Option<Decimal>, <D as Deserializer<'de>>::Error>
where
    D: Deserializer<'de>,

Deserializes an optional Decimal from a string field.

Returns None if the string is empty or “0”, otherwise parses to Decimal. This is a strict string-only deserializer; for flexible handling of strings, numbers, and null, use [deserialize_optional_decimal].

Errors

Returns an error if the string cannot be parsed as a valid decimal.