Unable to filter out null objects if referenced by encoding

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "description": "Unable to truly filter data",
  "data": {
    "values":[
      {
        "date": "2000-01-01"
      },
      {
        "date": "2000-02-01",
        "options": {
          "price": 16 
        }
      },
      {
        "date": "2000-03-01",
        "options": {
          "price": 17 
        }
      } 
    ]
  },
  "transform": [{"filter": "datum.options != null"}],
  "mark": "line",
  "encoding": {
    "x": {"field": "date", "type": "temporal", "axis": {"format": "%Y"}},
    "y": {"field": "options.price", "type": "quantitative"}
  }
}

This will throw “ERROR TypeError: Cannot read property ‘price’ of undefined” in the console. I’m not sure why “options.price” would ever try to be evaluated for the record which was supposed to be filtered out.

[LucidObscurity]

Nice. I do love the simplicity of Vega-Lite for most scenarios.

[domoritz]