Pie chart split chart by date is broken

[lukasolson]

1. Create a pie chart
2. Split chart by date histogram
3. Apply

Here is the error message in the console:

TypeError: Cannot read property 'id' of undefined
    at http://localhost:8000/components/agg_response/hierarchical/build_hierarchical_data.js:56:57
    at Function.map (http://localhost:8000/bower_components/lodash/dist/lodash.js:3508:27)
    at Object.hierarchical (http://localhost:8000/components/agg_response/hierarchical/build_hierarchical_data.js:54:22)
    at Renderbot.tables [as buildChartData] (http://localhost:8000/plugins/vis_types/vislib/_build_chart_data.js:11:28)
    at Renderbot.VislibRenderbot.render (http://localhost:8000/plugins/vis_types/vislib/_vislib_renderbot.js:38:28)
    at Object.<anonymous> (http://localhost:8000/components/visualize/visualize.js:108:28)
    at Object.fn (http://localhost:8000/components/visualize/visualize.js:57:18)
    at Scope.$get.Scope.$digest (http://localhost:8000/bower_components/angular/angular.js:12541:29)
    at Scope.$get.Scope.$apply (http://localhost:8000/bower_components/angular/angular.js:12806:24)
    at done (http://localhost:8000/bower_components/angular/angular.js:8379:45)

[spalger]

Unable to reproduce missed the fact you were splitting the chart

[spalger]

Looks like this happens anytime that you put a split chart agg as the only agg for a pie chart. I'd say that this is a bug we can fix after beta 3 since splitting charts without creating any slices is useless anyway. Wish there was better error reporting though. We should be fataling on that error rather than silently logging to the console.

[spalger]

@lukasolson Can you review the PR I just assigned you?