warning on timeField makes barchart not render anything

[rlgomes]

The barchart example from our documentation: http://juttle.github.io/juttle-viz/charts/barchart/ which is the following juttle:

read stochastic -source 'cdn' -nhosts 10 -from :10 minutes before 2014-01-01: -to :2014-01-01: -source_type 'metrics' name = 'cpu'
| filter name = 'cpu'
| reduce value = avg(value) by host
| sort value -desc
| view barchart -o {
    categoryField: 'host',
    valueField: 'value',
    title: 'Average CPU % per host for last 10 minutes',
    yScales: {
      primary: {
        tickFormat: '%'
      }
    },
    tooltip: {
      valueFormat: '%'
    }
  }

This didn't produce a warning at all (or maybe I didn't notice it ) but it did in fact produce the expected bars and now there's the warning "The "timeField" you specified does not contain valid values." and the SVG element with the barchart has the display set to none.