Function deserialize_optional_decimal_from_str 

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

Deserializes an optional Decimal from a string-only field.

Returns None if the value is null or the string is empty, otherwise parses to Decimal.

Errors

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