error on example "MapTable: Only Table and filters - sorting, virtual columns"

On the [MapTable: Only Table and filters - sorting, virtual columns](https://bl.ocks.org/melalj/ef85eb677583647daf52) example page, there's a JS error:

```
TypeError: null has no properties  maptable.min.js:2:16611
```

this causes the example to fail to render