Fix issue where null would be passed to explode

See merge request !5

Use `=== ''` instead of `empty()`

See merge request extensions/wsarrays!4

Make sure the entire array is associative

See merge request extensions/wsarrays!3

We need to put this check at the start of the function, to make sure the entire array is associative before removing any elements from the array.

Reset array indexing after unsetting an element

See merge request extensions/wsarrays!1