I'm trying to merge array2 into array1, so that empty fields stay like array1 and fields with value get overwritten at array1 from array2. But only empty fields, if it's null it should be treated as a number and overwrite a field. Please look at the two comments for a better understanding of what I mean.

**What I have tried:**

```js
const array1 = [[2], [], [3,5], [], [1]]
const array2 = [[], [], [4], [], [null]]

Array.prototype.splice.apply(array1, [0, array2.length].concat(array2))
console.log(array2)

// this logs [[], [], [4], [], [null]]

// what is should log is [[2], [], [4,5], [], [null]]
```