How can I merge two arrays:

```
$arr1 = [1 => 'a', 2 => '', 3 => 'c'];
$arr2 = [1 => 'd', 2 => 'e', 3 => 'f'];

```

and get:

```
[1 => 'a', 2 => 'e', 3 => 'c'];

```

I have done it succesfully with:

```
$arr1 = [1 => 'a',           3 => 'c'];
$arr2 = [1 => 'd', 2 => 'e', 3 => 'f'];

$arr1 + $arr2;

```

But, sometimes $arr1 also contains value `2 => ''` which is empty but present and in this case key `2` will not be overwriten by `$arr2`.