#vulnerable code 
                                private void loadResource(Yaml yaml, InputStream yamlStream, String filename) {
        Node loadedYaml = yaml.compose(new UnicodeReader(yamlStream));

        if (loadedYaml == null) {
            LOG.error("The file {} is empty", filename);
            return;
        }

        // Get and check top level config
        if (!(loadedYaml instanceof MappingNode)) {
            fail(loadedYaml, filename, "File must be a Map");
        }

        MappingNode rootNode = (MappingNode) loadedYaml;

        NodeTuple configNodeTuple = null;
        for (NodeTuple tuple : rootNode.getValue()) {
            String name = getKeyAsString(tuple, filename);
            if ("config".equals(name)) {
                configNodeTuple = tuple;
                break;
            }
        }

        String configKeyName = getKeyAsString(configNodeTuple, filename);
        if (!configKeyName.equals("config")) {
            fail(loadedYaml, filename, "The top level entry MUST be 'config'.");
        }

        SequenceNode configNode = getValueAsSequenceNode(configNodeTuple, filename);
        List<Node> configList = configNode.getValue();

        for (Node configEntry : configList) {
            if (!(configEntry instanceof MappingNode)) {
                fail(loadedYaml, filename, "The entry MUST be a mapping");
            }

            NodeTuple entry = getExactlyOneNodeTuple((MappingNode) configEntry, filename);
            MappingNode actualEntry = getValueAsMappingNode(entry, filename);
            String entryType = getKeyAsString(entry, filename);
            switch (entryType) {
                case "lookup":
                    loadYamlLookup(actualEntry, filename);
                    break;
                case "matcher":
                    loadYamlMatcher(actualEntry, filename);
                    break;
                case "test":
                    loadYamlTestcase(actualEntry, filename);
                    break;
                default:
                    throw new InvalidParserConfigurationException(
                        "Yaml config.(" + filename + ":" + actualEntry.getStartMark().getLine() + "): " +
                            "Found unexpected config entry: " + entryType + ", allowed are 'lookup, 'matcher' and 'test'");
            }
        }
    } 
                            #location 25 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                private void loadResource(Yaml yaml, InputStream yamlStream, String filename) {
        Node loadedYaml = yaml.compose(new UnicodeReader(yamlStream));

        if (loadedYaml == null) {
            throw new InvalidParserConfigurationException("The file " + filename + " is empty");
        }

        // Get and check top level config
        if (!(loadedYaml instanceof MappingNode)) {
            fail(loadedYaml, filename, "File must be a Map");
        }

        MappingNode rootNode = (MappingNode) loadedYaml;

        NodeTuple configNodeTuple = null;
        for (NodeTuple tuple : rootNode.getValue()) {
            String name = getKeyAsString(tuple, filename);
            if ("config".equals(name)) {
                configNodeTuple = tuple;
                break;
            }
        }

        if (configNodeTuple == null) {
            fail(loadedYaml, filename, "The top level entry MUST be 'config'.");
        }

        SequenceNode configNode = getValueAsSequenceNode(configNodeTuple, filename);
        List<Node> configList = configNode.getValue();

        for (Node configEntry : configList) {
            if (!(configEntry instanceof MappingNode)) {
                fail(loadedYaml, filename, "The entry MUST be a mapping");
            }

            NodeTuple entry = getExactlyOneNodeTuple((MappingNode) configEntry, filename);
            MappingNode actualEntry = getValueAsMappingNode(entry, filename);
            String entryType = getKeyAsString(entry, filename);
            switch (entryType) {
                case "lookup":
                    loadYamlLookup(actualEntry, filename);
                    break;
                case "matcher":
                    loadYamlMatcher(actualEntry, filename);
                    break;
                case "test":
                    loadYamlTestcase(actualEntry, filename);
                    break;
                default:
                    throw new InvalidParserConfigurationException(
                        "Yaml config.(" + filename + ":" + actualEntry.getStartMark().getLine() + "): " +
                            "Found unexpected config entry: " + entryType + ", allowed are 'lookup, 'matcher' and 'test'");
            }
        }
    }