The code works for TypeScript, but it causes errors when used with code generated by TSTL.

const obj = { key: 1 }
const num = Math.random()
const a = 0 // 0, 0.5, 1
const b = { ...(num < a && obj) }

generates

obj = {key = 1}
num = math.random()
a = 0
b = __TS__ObjectAssign({}, num < a and obj)

playground

https://typescripttolua.github.io/play/#code/5.4/MYewdgzgLgBCBGArGBeGBvGBrApgTwC4YBGGAXwChRJYwBXAW1RgFkBDKACwDoAnNsABMQDABQBKKuGgw2zAAwwA9EpjyANGu4BWTcSk0Y8Zpm5nR9JgB5ZMAGR24SceQpA