DataTable, findNextEditableColumn throws exception when using tab from the last cell in the grid

[dschmitz-gsits]

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Plunkr Case (Bug Reports)

http://plnkr.co/edit/f4yYapk4PQoUEL4VXu6V

Current behavior
If you select the cell with the value "2018" in the plnkr above and hit the "tab"-key you will observe this error:

Cannot read property 'classList' of null"

Expected behavior
No exception should be thrown if there is no next cell available.

A simple resolution should be to just add the following at this point:
https://github.com/primefaces/primeng/blob/master/components/datatable/datatable.ts#L1604

... } else { return; }

• PrimeNG version: primeng@4.0.0-rc.3