Show null values as a gap in vega line charts

Question

How can I show a gap instead of what seems to be the maximum value in this line chart? The highlighted segments should be replaced with a gap as y = null for x = 4 and c = 0 (the blue line).

{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "description": "A basic line chart example.",
  "width": 500,
  "height": 200,
  "padding": 5,

  "data": [
    {
      "name": "table",
      "values": [
        {"x": 0, "y": 28, "c":0}, {"x": 0, "y": 20, "c":1},
        {"x": 1, "y": 43, "c":0}, {"x": 1, "y": 35, "c":1},
        {"x": 2, "y": 81, "c":0}, {"x": 2, "y": 10, "c":1},
        {"x": 3, "y": 19, "c":0}, {"x": 3, "y": 15, "c":1},
        {"x": 4, "y": null, "c":0}, {"x": 4, "y": 48, "c":1},
        {"x": 5, "y": 24, "c":0}, {"x": 5, "y": 28, "c":1},
        {"x": 6, "y": 87, "c":0}, {"x": 6, "y": 66, "c":1},
        {"x": 7, "y": 17, "c":0}, {"x": 7, "y": 27, "c":1},
        {"x": 8, "y": 68, "c":0}, {"x": 8, "y": 16, "c":1},
        {"x": 9, "y": 49, "c":0}, {"x": 9, "y": 25, "c":1}
      ]
    }
  ],

  "scales": [
    {
      "name": "x",
      "type": "point",
      "range": "width",
      "domain": {"data": "table", "field": "x"}
    },
    {
      "name": "y",
      "type": "linear",
      "range": "height",
      "nice": true,
      "zero": true,
      "domain": {"data": "table", "field": "y"}
    },
    {
      "name": "color",
      "type": "ordinal",
      "range": "category",
      "domain": {"data": "table", "field": "c"}
    }
  ],

  "axes": [
    {"orient": "bottom", "scale": "x"},
    {"orient": "left", "scale": "y"}
  ],

  "marks": [
    {
      "type": "group",
      "from": {
        "facet": {
          "name": "series",
          "data": "table",
          "groupby": "c"
        }
      },
      "marks": [
        {
          "type": "line",
          "from": {"data": "series"},
          "encode": {
            "enter": {
              "x": {"scale": "x", "field": "x"},
              "y": {"scale": "y", "field": "y"},
              "stroke": {"scale": "color", "field": "c"},
              "strokeWidth": {"value": 2}
            },
            "update": {
              "strokeOpacity": {"value": 1}
            },
            "hover": {
              "strokeOpacity": {"value": 0.5}
            }
          }
        }
      ]
    }
  ]
}

Answer 1

Use the defined property.

{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "description": "A basic line chart example.",
  "width": 500,
  "height": 200,
  "padding": 5,
  "data": [
    {
      "name": "table",
      "values": [
        {"x": 0, "y": 28, "c": 0},
        {"x": 0, "y": 20, "c": 1},
        {"x": 1, "y": 43, "c": 0},
        {"x": 1, "y": 35, "c": 1},
        {"x": 2, "y": 81, "c": 0},
        {"x": 2, "y": 10, "c": 1},
        {"x": 3, "y": 19, "c": 0},
        {"x": 3, "y": 15, "c": 1},
        {"x": 4, "y": null, "c": 0},
        {"x": 4, "y": 48, "c": 1},
        {"x": 5, "y": 24, "c": 0},
        {"x": 5, "y": 28, "c": 1},
        {"x": 6, "y": 87, "c": 0},
        {"x": 6, "y": 66, "c": 1},
        {"x": 7, "y": 17, "c": 0},
        {"x": 7, "y": 27, "c": 1},
        {"x": 8, "y": 68, "c": 0},
        {"x": 8, "y": 16, "c": 1},
        {"x": 9, "y": 49, "c": 0},
        {"x": 9, "y": 25, "c": 1}
      ]
    }
  ],
  "scales": [
    {
      "name": "x",
      "type": "point",
      "range": "width",
      "domain": {"data": "table", "field": "x"}
    },
    {
      "name": "y",
      "type": "linear",
      "range": "height",
      "nice": true,
      "zero": true,
      "domain": {"data": "table", "field": "y"}
    },
    {
      "name": "color",
      "type": "ordinal",
      "range": "category",
      "domain": {"data": "table", "field": "c"}
    }
  ],
  "axes": [
    {"orient": "bottom", "scale": "x"},
    {"orient": "left", "scale": "y"}
  ],
  "marks": [
    {
      "type": "group",
      "from": {"facet": {"name": "series", "data": "table", "groupby": "c"}},
      "marks": [
        {
          "type": "line",
          "from": {"data": "series"},
          "encode": {
            "enter": {
              "x": {"scale": "x", "field": "x"},
              "y": {"scale": "y", "field": "y"},
              "stroke": {"scale": "color", "field": "c"},
              "strokeWidth": {"value": 2},
              "defined": {
                "signal": "isValid(datum[\"x\"]) && isFinite(+datum[\"x\"]) && isValid(datum[\"y\"]) && isFinite(+datum[\"y\"])"
              }
            },
            "update": {"strokeOpacity": {"value": 1}},
            "hover": {"strokeOpacity": {"value": 0.5}}
          }
        }
      ]
    }
  ]
}