Function deserialize_double_option_bytes 

pub fn deserialize_double_option_bytes<'de, D>(
    deserializer: D,
) -> Result<Option<Option<Vec<u8>>>, <D as Deserializer<'de>>::Error>
where
    D: Deserializer<'de>,

A patch-wrapped nullable Bytes field — Option<Option<Vec<u8>>>. The Bytes counterpart of crate::patch::deserialize_double_option (which can’t be reused: its T: Deserialize bound resolves to Vec<u8>’s strict blanket impl, the exact thing this module works around). Same contract — the outer Some records “this key was present”, so it must be paired with #[serde(default, …)].