Fix label and key that got swapped in refactor
Fix config for SORN grouped-timeseries graph
Fix grouped-timeseries config for tax disc and vehicle licensing
Swap `instanceof Array` for `_.isArray`

See http://nodejs.org/api/vm.html#vm_globals
grunt-jasmine executes specs in new vm contexts which break instanceof
Restrict null/undefined data defaulting to journey module

Graphs with undefined data were being erroneously flattened to zero then they should have been left undefined.