Assertion at runtime with await and json.to()

Code to reproduce:

import json, asyncdispatch

proc getData(): Future[JsonNode] {.async.} = 
  result = %*{"value": 1}

type 
  MyData = object
    value: BiggestInt

proc main() {.async.} = 
  let data = to(await(getData()), MyData)
  echo data

waitFor(main())

It works if you change let data = to(await getData(), MyData) to

let raw = await(getData())
let data = to(raw, MyData)

It also works with Nim 0.18.0 (that's why I call it a regression), and I think that it started happening after last PRs related to async.

Error stacktrace (click to open)

test.nim(14)             test
asyncmacro.nim(304)      main
asyncmacro.nim(36)       main_continue
json.nim(1429)           mainIter
json.nim(426)            []
system.nim(3800)         failedAssertImpl
system.nim(3793)         raiseAssert
system.nim(2847)         sysFatal
[[reraised from:
test.nim(14)             test
asyncdispatch.nim(1649)  waitFor
asyncfutures.nim(302)    read
]]
Error: unhandled exception: not isNil(node)
Async traceback:
  test.nim(14)        test
  asyncmacro.nim(304) main
  asyncmacro.nim(36)  main_continue
    ## Resumes an async procedure
  json.nim(1429)      mainIter
  json.nim(426)       []
  system.nim(3800)    failedAssertImpl
  system.nim(3793)    raiseAssert
  system.nim(2847)    sysFatal
Exception message: not isNil(node)
Exception type: [AssertionError]
Error: execution of an external program failed: '/Users/dian/Projects/nickel/src/test '