router.call doesn't work with buffer

[d-enk]

OK

local buf = require("buffer").ibuf()

local future = vshard.router.route(1):callro("box.info", {}, {buffer = buf, is_async= true})

local size = future:wait_result()

return require("msgpack").decode(buf.rpos, size)

BUT

vshard.router.callro(1, "box.info", {}, {buffer = require("buffer").ibuf()})

- null # no size

vshard.router.callro(1, "box.info", {}, {buffer = require("buffer").ibuf(), is_async= true }):wait_result()

- error: '.../tarantool/.rocks/share/tarantool/vshard/router/init.lua:479: attempt
    to index local ''res'' (a number value)