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BoxChart rejects valid List.of data with NullPointerException

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@PHJ2000 is already working on this.

Since Oct 5, 2026.

  • #1033 by @PHJ2000 — open

Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
76/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
java
Domain
data-visualization

Research direction

Start by reading the validation paths used by BoxChart.addSeries, series.replaceData, and chart.updateBoxSeries; the issue identifies all three entry points. Add or update tests for two- and three-element List.of inputs, replacement/update, and lists containing null. Done means null-free immutable lists are accepted and lists with null elements remain rejected.

Written by the indexing model from the issue text.

Description

Describe the bug
BoxChart rejects valid, null-free lists created with List.of(...). Both adding a series and replacing its data throw NullPointerException because the validation calls contains(null), which these lists do not support.

To Reproduce

import java.util.List;
import org.knowm.xchart.BoxChart;
import org.knowm.xchart.BoxChartBuilder;
import org.knowm.xchart.SwingWrapper;

public class ImmutableBoxData {
  public static void main(String[] args) {
    new SwingWrapper<>(getChart()).displayChart();
  }

  public static BoxChart getChart() {
    BoxChart chart = new BoxChartBuilder().width(640).height(480).build();
    chart.addSeries("sample", List.of(1, 2, 3)); // NullPointerException
    return chart;
  }
}

The same exception occurs when calling series.replaceData(List.of(4, 5)) or chart.updateBoxSeries(...) on an existing series.

Expected behavior
Accept the null-free lists while continuing to reject lists that actually contain null elements.

Reproduced on 4.0.5-SNAPSHOT, Java 11. The exception happens before rendering, so no screenshot is needed. Tests cover two- and three-element immutable lists, replacement/update, and rejection of actual null elements.

Dominant language
Java
Stars
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Forks
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First steps

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  4. Open a pull request that references the issue number.

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