#vulnerable code 
                              @Test
  public void testDetectDuplicateMapping() throws Exception {
    MappingFileReader fileReader = new MappingFileReader("duplicateMapping.xml");
    MappingFileData mappingFileData = fileReader.read();
    try {
      parser.processMappings(mappingFileData.getClassMaps(), new Configuration());
      fail("should have thrown exception");
    } catch (Exception e) {
      assertTrue("invalid exception", e.getMessage().indexOf("Duplicate Class Mapping Found") != -1);
    }
  } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                              @Test
  public void testDetectDuplicateMapping() throws Exception {
    MappingFileReader fileReader = new MappingFileReader(XMLParserFactory.getInstance());
    MappingFileData mappingFileData = fileReader.read("duplicateMapping.xml");
    try {
      parser.processMappings(mappingFileData.getClassMaps(), new Configuration());
      fail("should have thrown exception");
    } catch (Exception e) {
      assertTrue("invalid exception", e.getMessage().indexOf("Duplicate Class Mapping Found") != -1);
    }
  }