#vulnerable code 
                                @Test
    public void testValuesInFlow() throws Exception {
        // compile
        URI resource = getClass().getResource("/yaml/formats/values_flow.sl").toURI();
        URI operation = getClass().getResource("/yaml/formats/values_op.sl").toURI();

        SlangSource dep = SlangSource.fromFile(operation);
        Set<SlangSource> path = Sets.newHashSet(dep);
        CompilationArtifact compilationArtifact = slang.compile(SlangSource.fromFile(resource), path);

        // trigger
        Map<String, Serializable> userInputs = new HashMap<>();
        userInputs.put("input_no_expression", "input_no_expression_value");
        userInputs.put("input_overridable", "i_should_not_be_assigned");
        Map<String, Serializable> systemProperties = new HashMap<>();
        systemProperties.put("user.sys.props.host", "localhost");

        Map<String, StepData> steps = triggerWithData(compilationArtifact, userInputs, systemProperties).getTasks();

        // verify
        StepData flowData = steps.get(EXEC_START_PATH);
        StepData taskData = steps.get(FIRST_STEP_PATH);

        verifyFlowInputs(flowData);
        verifyFlowOutputs(flowData);
        verifyTaskInputs(taskData);
        verifyTaskPublishValues(taskData);
        verifyExecutableResult(flowData);
    } 
                            #location 27 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Test
    public void testValuesInFlow() throws Exception {
        // compile
        URI resource = getClass().getResource("/yaml/formats/values_flow.sl").toURI();
        URI operation1 = getClass().getResource("/yaml/formats/values_op.sl").toURI();
        URI operation2 = getClass().getResource("/yaml/noop.sl").toURI();

        SlangSource dep1 = SlangSource.fromFile(operation1);
        SlangSource dep2 = SlangSource.fromFile(operation2);
        Set<SlangSource> path = Sets.newHashSet(dep1, dep2);
        CompilationArtifact compilationArtifact = slang.compile(SlangSource.fromFile(resource), path);

        // trigger
        Map<String, Serializable> userInputs = new HashMap<>();
        userInputs.put("input_no_expression", "input_no_expression_value");
        userInputs.put("input_overridable", "i_should_not_be_assigned");
        Map<String, Serializable> systemProperties = new HashMap<>();
        systemProperties.put("user.sys.props.host", "localhost");

        Map<String, StepData> steps = triggerWithData(compilationArtifact, userInputs, systemProperties).getTasks();

        // verify
        StepData flowData = steps.get(EXEC_START_PATH);
        StepData taskData = steps.get(FIRST_STEP_PATH);
        StepData oneLinerTaskData = steps.get(SECOND_STEP_KEY);

        verifyFlowInputs(flowData);
        verifyFlowOutputs(flowData);
        verifyTaskInputs(taskData);
        verifyTaskPublishValues(taskData);
        verifyOneLinerInputs(oneLinerTaskData);
        verifyExecutableResult(flowData);
    }