Function encode_nested_value 

fn encode_nested_value(
    key: u64,
    value: &KvpValue,
    out: &mut Vec<u8>,
) -> Result<(), FillError>

Write one nested parameter’s value in the shape its type names.

The shapes are Table 6’s eight types only, which is the whole of what may be nested; anything else was refused by FillParameters::with before it got here.