Function get_field_optional 

pub fn get_field_optional<T: FromLedger, const CODE: i32>(
    slot: i32,
    field: SField<T, CODE>,
) -> Result<Option<T>>

Retrieves an optionally present field from the ledger object cached in slot.

Returns

Returns a Result<Option<T>> where:

• Ok(Some(T)) - The field value for the specified field
• Ok(None) - If the field is not present (i.e., result_code == FIELD_NOT_FOUND)
• Err(Error) - If the field cannot be retrieved, has unexpected size, or fails to decode