#vulnerable code 
                                @Nonnull
    private static RoleMap retrieveRoleMap(@Nonnull CNode config, @Nonnull String name, Configurator<RoleDefinition> configurator) throws ConfiguratorException {
        Mapping map = config.asMapping();
        final Sequence c = map.get(name).asSequence();

        TreeMap<Role, Set<String>> resMap = new TreeMap<>();
        if (c == null) {
            // we cannot return emptyMap here due to the Role Strategy code
            return new RoleMap(resMap);
        }

        for (CNode entry : c) {
            RoleDefinition definition = configurator.configure(entry);
            resMap.put(definition.getRole(), definition.getAssignments());
        }

        return new RoleMap(resMap);
    } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Nonnull
    private static RoleMap retrieveRoleMap(@Nonnull CNode config, @Nonnull String name, Configurator<RoleDefinition> configurator) throws ConfiguratorException {
        Mapping map = config.asMapping();
        final CNode c = map.get(name);

        TreeMap<Role, Set<String>> resMap = new TreeMap<>();
        if (c == null || c.asSequence() == null) {
            // we cannot return emptyMap here due to the Role Strategy code
            return new RoleMap(resMap);
        }

        for (CNode entry : c.asSequence()) {
            RoleDefinition definition = configurator.configure(entry);
            resMap.put(definition.getRole(), definition.getAssignments());
        }

        return new RoleMap(resMap);
    }