#vulnerable code 
                                @Test
    public void getVersionOnTopicWithVersionBeforeRIDGets() throws IOException
    {
        //arrange
        String validString = "$iothub/twin/res/?$version=7&$rid=5";
        TopicParser testParser = new TopicParser(validString);

        //act
        String version = testParser.getVersion(3);

        //assert
        assertNotNull(version);
        assertTrue(version.equals(String.valueOf(7)));

    } 
                            #location 13 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Test
    public void getVersionOnTopicWithVersionBeforeRIDGets() throws IOException
    {
        //arrange
        String validString = "$iothub/twin/res/?$version=7&$rid=5";
        TopicParser testParser = new TopicParser(validString);

        //act
        String version = Deencapsulation.invoke(testParser, "getVersion", 3);

        //assert
        assertNotNull(version);
        assertTrue(version.equals(String.valueOf(7)));

    }