Steps to Reproduce

1. run

    <button onClick="setEmptyData()"/>
    <charts id="chart"/>
    <zscript><![CDATA[
    import org.zkoss.chart.*;

public void setEmptyData(){
    chart.getSeries().setData(new Point[0]);
}
    ]]></zscript>

2. click the button

Current Result

• click 1st time
  TypeError: this.addSeries is not a function

• click the 2nd time
  TypeError: Cannot read properties of undefined (reading '0')

Expected Result

no error

Debug Information

• key statement chart.getSeries().setData(new Point[0]);
• the original use case:
  The dev doesn't plan to pass an empty array on purpose. He creates an array from a query result

  Point[] pointArray = new Point[queryResult];
  chart.getSeries().setData(pointArray);
  

Propose solution

The method should check the size and render nothing for an empty array. So this will benefit callers.