Jasper Reports - error Unexpected EOF in prolog when using Chart Theme - jasper-reports

Question

I need to build a new chart theme for a Line Chart. To do that I followed all the steps specified in this tutorial Chart Themes
To apply the theme in Jasper Studio I select the chart and I navigate to Properties -> Chart -> Here I select the name of the new theme from the Theme dropdown. After that I try to Preview the report. When I do this I get this error message:
net.sf.jasperreports.engine.JRException: net.sf.jasperreports.util.JacksonRuntimException: com.fasterxml.jackson.core.JsonParseException: Unexpected EOF in prolog
at [row,col {unknown-source}]: [1,0]
at com.jaspersoft.studio.editor.preview.view.control.ReportController.fillReport(ReportController.java:553)
at com.jaspersoft.studio.editor.preview.view.control.ReportController.access$18(ReportController.java:528)
at com.jaspersoft.studio.editor.preview.view.control.ReportController$1.run(ReportController.java:446)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)
Caused by: net.sf.jasperreports.util.JacksonRuntimException: com.fasterxml.jackson.core.JsonParseException: Unexpected EOF in prolog
at [row,col {unknown-source}]: [1,0]
at net.sf.jasperreports.util.JacksonUtil.loadXml(JacksonUtil.java:215)
at net.sf.jasperreports.chartthemes.simple.XmlChartTheme.loadSettings(XmlChartTheme.java:131)
at net.sf.jasperreports.chartthemes.simple.XmlChartTheme.loadSettings(XmlChartTheme.java:104)
at net.sf.jasperreports.chartthemes.simple.XmlChartTheme.getChartThemeSettings(XmlChartTheme.java:88)
at net.sf.jasperreports.chartthemes.simple.SimpleChartTheme.getChartSettings(SimpleChartTheme.java:212)
at net.sf.jasperreports.chartthemes.simple.SimpleChartTheme.configureChart(SimpleChartTheme.java:443)
at net.sf.jasperreports.chartthemes.simple.SimpleChartTheme.createLineChart(SimpleChartTheme.java:1001)
at net.sf.jasperreports.chartthemes.simple.SimpleChartTheme.createChart(SimpleChartTheme.java:387)
at net.sf.jasperreports.engine.fill.JRFillChart.evaluateChart(JRFillChart.java:846)
at net.sf.jasperreports.engine.fill.JRFillChart.evaluateRenderer(JRFillChart.java:799)
at net.sf.jasperreports.engine.fill.JRFillChart.resolveElement(JRFillChart.java:1407)
at net.sf.jasperreports.engine.fill.JRFillElement.performDelayedEvaluation(JRFillElement.java:1140)
at net.sf.jasperreports.engine.fill.JRFillElement.resolveElement(JRFillElement.java:1242)
at net.sf.jasperreports.engine.fill.ElementEvaluationAction.execute(ElementEvaluationAction.java:69)
at net.sf.jasperreports.engine.fill.DelayedFillActions.runActions(DelayedFillActions.java:271)
at net.sf.jasperreports.engine.fill.BaseReportFiller.resolveBoundElements(BaseReportFiller.java:807)
at net.sf.jasperreports.engine.fill.JRBaseFiller.resolveReportBoundElements(JRBaseFiller.java:1209)
at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillSummary(JRVerticalFiller.java:1238)
at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReportEnd(JRVerticalFiller.java:308)
at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReport(JRVerticalFiller.java:126)
at net.sf.jasperreports.engine.fill.JRBaseFiller.fill(JRBaseFiller.java:622)
at net.sf.jasperreports.engine.fill.BaseFillHandle$ReportFill.run(BaseFillHandle.java:135)
at java.base/java.lang.Thread.run(Unknown Source)
Caused by: com.fasterxml.jackson.core.JsonParseException: Unexpected EOF in prolog
at [row,col {unknown-source}]: [1,0]
at com.fasterxml.jackson.dataformat.xml.XmlFactory._initializeXmlReader(XmlFactory.java:717)
at com.fasterxml.jackson.dataformat.xml.XmlFactory._createParser(XmlFactory.java:583)
at com.fasterxml.jackson.dataformat.xml.XmlFactory._createParser(XmlFactory.java:30)
at com.fasterxml.jackson.core.JsonFactory.createParser(JsonFactory.java:1083)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3666)
at net.sf.jasperreports.util.JacksonUtil.loadXml(JacksonUtil.java:211)
... 22 more
Caused by: com.ctc.wstx.exc.WstxEOFException: Unexpected EOF in prolog
at [row,col {unknown-source}]: [1,0]
at com.ctc.wstx.sr.StreamScanner.throwUnexpectedEOF(StreamScanner.java:701)
at com.ctc.wstx.sr.BasicStreamReader.handleEOF(BasicStreamReader.java:2235)
at com.ctc.wstx.sr.BasicStreamReader.nextFromProlog(BasicStreamReader.java:2141)
at com.ctc.wstx.sr.BasicStreamReader.next(BasicStreamReader.java:1180)
at com.fasterxml.jackson.dataformat.xml.XmlFactory._initializeXmlReader(XmlFactory.java:712)
... 27 more
at [row,col {unknown-source}]: [1,0]
I don't know what to do about this error. If I select another Theme from the Theme dropdown (a default theme) it works just fine. Can someone help me with this problem? Thank you!