Line is broken if items have names and there are null values in series

[vaadin-bot]

Originally by Jonas Granvik

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Line is broken and becomes a scatter line if items have name set AND there is a null value in data series.

#!java
        Date date = new Date();
        date.setDate(1);
        Series series = new DataSeries();
        series.setName("testseries");
        List<DataSeriesItem> items = new ArrayList<DataSeriesItem>();
        DataSeriesItem item = new DataSeriesItem(date, rand.nextInt());
        item.setName("buu1");
        items.add(item);
        item = new DataSeriesItem();
        date = new Date();
        date.setDate(2);
        item.setX(date);
        item.setY(rand.nextInt());
        item.setName("buu2");
        item.setY((Double)null);
        items.add(item);
        date = new Date();
        date.setDate(3);
        item = new DataSeriesItem(date, rand.nextInt());
        item.setName("buu3");
        items.add(item);
        date = new Date();
        date.setDate(4);
        item = new DataSeriesItem(date, rand.nextInt());
        item.setName("buu4");
        items.add(item);
        ((DataSeries) series).setData(items);
        conf.addSeries(series);

The following JSON is produced which shows that the y-value is totally missing (not null) in series

{
  "chart": {
    "type": "line"
  },
  "title": {
    "text": ""
  },
  "plotOptions": {
    "line": {
      "stacking": ""
    }
  },
  "series": [
    {
      "data": [
        {
          "name": "buu1",
          "y": 519935669,
          "x": 1367405310087,
          "customized": true
        },
        {
          "name": "buu2",
          "x": 1367491710088,
          "customized": true
        },
        {
          "name": "buu3",
          "y": 459002652,
          "x": 1367578110088,
          "customized": true
        },
        {
          "name": "buu4",
          "y": -1079744054,
          "x": 1367664510088,
          "customized": true
        }
      ],
      "name": "testseries",
      "visible": true
    }
  ],
  "exporting": {
    "enabled": false
  }
}

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Imported from https://dev.vaadin.com/ issue #11941

[vaadin-bot]

Originally by @mstahv

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Fixing this requires a bit ugly hack to code until #12038. The project that found the issue, found out that names where irrelevant for them so lowering priority. We'll re-consider quick ugly fix in maintenance release if somebody else finds this important (e.g. via pro bug fix priority).

[vaadin-bot]

Originally by @zch

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This issue is present for all chart types with data series containing null values.

[vaadin-bot]

Originally by @zch

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We don't have time to do #12038 for 2.0, and there's not much point in making an ugly hack right now.