This PR adds support for arrays with empty elements e.g. `["", false, , , ]`. Before we were filling the empty places with `undefined`, but this is wrong according to [spec](https://tc39.es/ecma262/#sec-runtime-semantics-arrayaccumulation) there shouldn't be undefined with a index at that place, instead only `length` is incremented. So `[,,,].length == 3` and operations like `[,,,,].indexOf(undefined) == -1`, `[,,,,].lastIndexOf(undefined) == -1` etc.
Halid Odat
ada4ca895f