The flowable dmn is generated as a picture

1

Hi, everyone.I want to generate the flowable dmn into a picture, using the official interface, the generated png content is empty. Do you have any suggestions?
Below is the Java code for the call

 DefaultDecisionRequirementsDiagramGenerator diagramGenerator = new DefaultDecisionRequirementsDiagramGenerator();
        DmnDecision dmnDecision = dmnRepositoryService.createDecisionQuery().decisionVersion(Integer.valueOf(decisionVersion)).decisionKey(decisionKey).singleResult();
        DmnDefinition dmnDefinition = dmnRepositoryService.getDmnDefinition(dmnDecision.getId());
        DmnEngineConfiguration engineConfiguration = dmnEngine.getDmnEngineConfiguration();
        String decisionFontName = engineConfiguration.getDecisionFontName();
        String labelFontName = engineConfiguration.getLabelFontName();
        String annotationFontName = engineConfiguration.getAnnotationFontName();
        InputStream inputStream = diagramGenerator.generateDiagram(dmnDefinition,"png",decisionFontName,labelFontName,annotationFontName,engineConfiguration.getClassLoader(),2.0);
         try {
            File directory = new File("*******");
            if (!directory.exists()) {
                directory.mkdirs();
            }
            String fileName = "dmn-diagram.png";
            File file = new File(directory, fileName);
            OutputStream outputStream = null;
            outputStream = new FileOutputStream(file);

            byte[] buffer = new byte[1024];
            int length;
            while ((length = inputStream.read(buffer)) > 0) {
                outputStream.write(buffer, 0, length);
            }
            outputStream.close();
            inputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }

Below is the decision xml

<?xml version="1.0" encoding="UTF-8"?>
<definitions xmlns="https://www.omg.org/spec/DMN/20191111/MODEL/" xmlns:dmndi="https://www.omg.org/spec/DMN/20191111/DMNDI/" xmlns:biodi="http://bpmn.io/schema/dmn/biodi/2.0" xmlns:dc="http://www.omg.org/spec/DMN/20180521/DC/" id="definition_07cc22b4-c6f1-11ed-855f-0242ac110002" name="qqqqqq" namespace="http://www.flowable.org/dmn" exporter="Flowable Open Source Modeler" exporterVersion="6.8.0">
  <decision id="proc-zulkj2-jyolz7snh" name="Test decision sheet">
    <decisionTable id="decisionTable_5317662c-1702-454b-98f2-ee356f3ecf7d" hitPolicy="FIRST">
      <input label="name" biodi:width="379">
        <inputExpression id="inputExpression_e128905b-f9ca-4a4b-a810-b90e9b5dce66" typeRef="string">
          <text>name</text>
        </inputExpression>
        <inputValues>
          <text>"a","b","c"</text>
        </inputValues>
      </input>
      <output id="outputExpression_58ff96d0-0f3a-4139-99e1-1afe84c3ea97" label="outname" name="outname" typeRef="string">
        <outputValues>
          <text>"aa"</text>
        </outputValues>
      </output>
      <rule>
        <inputEntry id="inputEntry_e128905b-f9ca-4a4b-a810-b90e9b5dce66_1">
          <text>=="a"</text>
        </inputEntry>
        <outputEntry id="outputEntry_58ff96d0-0f3a-4139-99e1-1afe84c3ea97_1">
          <text>"aa"</text>
        </outputEntry>
      </rule>
    </decisionTable>
  </decision>
  <dmndi:DMNDI>
    <dmndi:DMNDiagram id="DMNDiagram_0l0hvq8">
      <dmndi:DMNShape id="DMNShape_14gn6g8" dmnElementRef="proc-zulkj2-jyolz7snh">
        <dc:Bounds height="80" width="180" x="-490" y="-190" />
      </dmndi:DMNShape>
    </dmndi:DMNDiagram>
  </dmndi:DMNDI>
</definitions>

image
image704×28 1.58 KB

How to solve this problem？
Thank you in advance.