title: net.sf.jasperreports.engine.JRRuntimeException: Category series name is null
body: <p>I want to display a simple report with a textfield : "hello world".</p>
  
  <p>The problem is i'm getting an error message category series name is null and i don't know why. Does anybody have a clue?</p>
  
  <p>The server log</p>
  
  <pre><code>net.sf.jasperreports.engine.JRRuntimeException: Category series name is null.
  at net.sf.jasperreports.charts.fill.JRFillCategoryDataset.customIncrement(JRFillCategoryDataset.java:142)
  at net.sf.jasperreports.engine.fill.JRFillElementDataset.increment(JRFillElementDataset.java:191)
  at net.sf.jasperreports.engine.fill.JRCalculator.calculateVariables(JRCalculator.java:183)
  at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillDetail(JRVerticalFiller.java:742)
  at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReportStart(JRVerticalFiller.java:262)
  at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReport(JRVerticalFiller.java:122)
  at net.sf.jasperreports.engine.fill.JRBaseFiller.fill(JRBaseFiller.java:551)
  at net.sf.jasperreports.engine.fill.BaseReportFiller.fill(BaseReportFiller.java:411)
  at net.sf.jasperreports.engine.fill.JRFillSubreport.fillSubreport(JRFillSubreport.java:732)
  at net.sf.jasperreports.engine.fill.JRSubreportRunnable.run(JRSubreportRunnable.java:58)
  at net.sf.jasperreports.engine.fill.AbstractThreadSubreportRunner.run(AbstractThreadSubreportRunner.java:216)
  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
  at java.lang.Thread.run(Thread.java:745)
  </code></pre>
  
  <p>printreport method:</p>
  
  <pre><code>public void printReport() throws JRException, IOException, NamingException, SQLException, ClassNotFoundException {
  
      System.setProperty("java.awt.headless", "true");
      File jasper = new File("/some/path/to/report.jasper");
      JasperPrint jasperPrint = JasperFillManager.fillReport(jasper.getPath(),new HashMap(), new JREmptyDataSource());        
      JasperExportManager.exportReportToPdfStream(jasperPrint, someOutputStream);
  }
  </code></pre>
  
  <p>jrxml file:</p>
  
  <pre><code>    &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;jasperReport xmlns="http://jasperreports.sourceforge.net/jasperreports" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://jasperreports.sourceforge.net/jasperreports http://jasperreports.sourceforge.net/xsd/jasperreport.xsd" name="report name" pageWidth="595" pageHeight="842" whenNoDataType="AllSectionsNoDetail" columnWidth="535" leftMargin="20" rightMargin="20" topMargin="20" bottomMargin="20" uuid="1119a425-bbc5-4d11-93a1-ab32daa4ccbc"&gt;
      &lt;property name="ireport.zoom" value="1.0"/&gt;
      &lt;property name="ireport.x" value="0"/&gt;
      &lt;property name="ireport.y" value="0"/&gt;
      &lt;background&gt;
          &lt;band splitType="Stretch"/&gt;
      &lt;/background&gt;
      &lt;title&gt;
          &lt;band height="79" splitType="Stretch"&gt;
              &lt;textField&gt;
                  &lt;reportElement x="254" y="22" width="100" height="20" uuid="a59aa154-093e-4330-8be7-515e56d76412"/&gt;
                  &lt;textFieldExpression&gt;&lt;![CDATA["HELLO WORLD"]]&gt;&lt;/textFieldExpression&gt;
              &lt;/textField&gt;
          &lt;/band&gt;
      &lt;/title&gt;
      &lt;pageHeader&gt;
          &lt;band height="35" splitType="Stretch"/&gt;
      &lt;/pageHeader&gt;
      &lt;columnHeader&gt;
          &lt;band height="61" splitType="Stretch"/&gt;
      &lt;/columnHeader&gt;
      &lt;detail&gt;
          &lt;band height="125" splitType="Stretch"/&gt;
      &lt;/detail&gt;
      &lt;columnFooter&gt;
          &lt;band height="45" splitType="Stretch"/&gt;
      &lt;/columnFooter&gt;
      &lt;pageFooter&gt;
          &lt;band height="54" splitType="Stretch"/&gt;
      &lt;/pageFooter&gt;
      &lt;summary&gt;
          &lt;band height="42" splitType="Stretch"/&gt;
      &lt;/summary&gt;
  &lt;/jasperReport&gt;
  </code></pre>