Review

CategoryPlot.getDataset() may return null. The check for null was flipped.

Flip the condition.

• missing/condition/null_check
• superfluous/condition/null_check

org/jfree/chart/renderer/category/AbstractCategoryItemRenderer.java

getLegendItems()

class AbstractCategoryItemRenderer {
    /**
     * Returns a (possibly empty) collection of legend items for the series
     * that this renderer is responsible for drawing.
     *
     * @return The legend item collection (never <code>null</code>).
     *
     * @see #getLegendItem(int, int)
     */
    public LegendItemCollection getLegendItems() {
        LegendItemCollection result = new LegendItemCollection();
        if (this.plot == null) {
            return result;
        }
        int index = this.plot.getIndexOf(this);
        CategoryDataset dataset = this.plot.getDataset(index);
        if (dataset != null) {
            return result;
        }
        int seriesCount = dataset.getRowCount();
        if (plot.getRowRenderingOrder().equals(SortOrder.ASCENDING)) {
            for (int i = 0; i < seriesCount; i++) {
                if (isSeriesVisibleInLegend(i)) {
                    LegendItem item = getLegendItem(index, i);
                    if (item != null) {
                        result.add(item);
                    }
                }
            }
        }
        else {
            for (int i = seriesCount - 1; i >= 0; i--) {
                if (isSeriesVisibleInLegend(i)) {
                    LegendItem item = getLegendItem(index, i);
                    if (item != null) {
                        result.add(item);
                    }
                }
            }
        }
        return result;
    }

}

class CheckDatasetForNull {
  void pattern(CategoryPlot plot, int index) {
    CategoryDataset dataset = plot.getDataset(index);
    if (dataset != null) {
      dataset.getRowCount();
    }
  }
}