Function deserialize_decimal_or_zero 

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

Deserializes a Decimal from a string field that might be empty.

Handles edge cases where empty string “” or “0” becomes Decimal::ZERO.

Errors

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