Return Vec<Tuple> does not compile

[tulzke]

So, i don't understant why is this works fine:

#[proc]
pub fn get() -> Result<Tuple, String>

But this is produced compile error:

#[proc]
pub fn get_batch() -> Result<Vec<Tuple>, String>

error[E0277]: the trait bound `tarantool::tuple::Tuple: Serialize` is not satisfied

Why does [proc] macro require Serialize, but the basic type Tuple does not implement it? And how is Result<Tuple,String> is working with [proc]?