Hello, I am a little confused with what I see (using the playground).

```
let x = ["a", "b", "c"]
let y = x[2] ++ " hi"
```

That compiles without error. After adding open Belt:

```
open Belt
let x = ["a", "b", "c"]
let y = x[2] ++ " hi"
```

I get the error:

[E] Line 3, column 8:

This has type: option<string>

Somewhere wanted: string

What changes?