See this Playground example.

class C {
    constructor(baz?: unknown) {
        print(`ctor: ${baz}`);
    }
}
const foo = new C;
const bar = new C();

If you look at the last two lines of transpiled Lua code:

foo = __TS__New(C, true)
bar = __TS__New(C)

We see foo has an additional argument true passed to the constructor.
I feel like this is a bug.