#vulnerable code 
                                @POST
    public FormValidation doCheckNewSource(@QueryParameter String newSource) {
        Jenkins.getInstance().checkPermission(Jenkins.ADMINISTER);
        String normalizedSource = Util.fixEmptyAndTrim(newSource);
        File file = new File(Util.fixNull(normalizedSource));
        if (normalizedSource == null) {
            return FormValidation.ok(); // empty, do nothing
        }
        if (!file.exists() && !ConfigurationAsCode.isSupportedURI(normalizedSource)) {
            return FormValidation.error("Configuration cannot be applied. File or URL cannot be parsed or do not exist.");
        }
        try {
            final Map<Source, String> issues = collectIssues(normalizedSource);
            final JSONArray errors = collectProblems(issues, "error");
            if (!errors.isEmpty()) {
                return FormValidation.error(errors.toString());
            }
            final JSONArray warnings = collectProblems(issues, "warning");
            if (!warnings.isEmpty()) {
                return FormValidation.warning(warnings.toString());
            }
            return FormValidation.okWithMarkup("The configuration can be applied");
        } catch (ConfiguratorException | IllegalArgumentException e) {
            return FormValidation.error(e, e.getCause() == null ? e.getMessage() : e.getCause().getMessage());
        }
    } 
                            #location 14 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @POST
    public FormValidation doCheckNewSource(@QueryParameter String newSource) {
        Jenkins.getInstance().checkPermission(Jenkins.ADMINISTER);
        String normalizedSource = Util.fixEmptyAndTrim(newSource);
        File file = new File(Util.fixNull(normalizedSource));
        if (normalizedSource == null) {
            return FormValidation.ok(); // empty, do nothing
        }
        if (!file.exists() && !ConfigurationAsCode.isSupportedURI(normalizedSource)) {
            return FormValidation.error("Configuration cannot be applied. File or URL cannot be parsed or do not exist.");
        }

        List<YamlSource> yamlSources = Collections.emptyList();
        try {
            List<String> sources = Collections.singletonList(normalizedSource);
            yamlSources = getConfigFromSources(sources);
            final Map<Source, String> issues = checkWith(yamlSources);
            final JSONArray errors = collectProblems(issues, "error");
            if (!errors.isEmpty()) {
                return FormValidation.error(errors.toString());
            }
            final JSONArray warnings = collectProblems(issues, "warning");
            if (!warnings.isEmpty()) {
                return FormValidation.warning(warnings.toString());
            }
            return FormValidation.okWithMarkup("The configuration can be applied");
        } catch (ConfiguratorException | IllegalArgumentException e) {
            return FormValidation.error(e, e.getCause() == null ? e.getMessage() : e.getCause().getMessage());
        } finally {
            closeSources(yamlSources);
        }
    }