Function decode_parameter_value 

fn decode_parameter_value(
    encoding: ParamEncoding,
    abs_key: u64,
    buf: &mut impl Buf,
) -> Result<KvpValue, CodecError>

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

Shared by the message’s own parameter block and by the nested block inside FILL_PARAMETERS, so a type cannot be read one way in a message and another way in a fill.