Function encode 

pub fn encode<'a, I>(out: &mut BytesMut, fields: I)
where
    I: IntoIterator<Item = (&'a [u8], &'a [u8])>,

Encodes a field section: the prefix, then one line per field.

The prefix is always 0x00 0x00 – Required Insert Count 0, Base 0 – which RFC 9204 §4.5.1 requires of a section that references no dynamic entry.