How to use the @0x/sol-resolver.RelativeFSResolver function in @0x/sol-resolver

const config: CompilerOptions = fs.existsSync(CONFIG_FILE)
            ? JSON.parse(fs.readFileSync(CONFIG_FILE).toString())
            : {};
        if (_.isUndefined(artifactsPath) && _.isUndefined(config.artifactsDir)) {
            throw new Error(`artifactsDir not found in ${CONFIG_FILE}`);
        }
        this._artifactsPath = (artifactsPath || config.artifactsDir) as string;
        if (_.isUndefined(sourcesPath) && _.isUndefined(config.contractsDir)) {
            throw new Error(`contractsDir not found in ${CONFIG_FILE}`);
        }
        this._sourcesPath = (sourcesPath || config.contractsDir) as string;
        this._resolver = new FallthroughResolver();
        this._resolver.appendResolver(new URLResolver());
        const packagePath = path.resolve('');
        this._resolver.appendResolver(new NPMResolver(packagePath));
        this._resolver.appendResolver(new RelativeFSResolver(this._sourcesPath));
        this._resolver.appendResolver(new FSResolver());
    }
    public async collectContractsDataAsync(): Promise {

...DEFAULT_COMPILER_SETTINGS,
            ...config.compilerSettings,
            ...passedOpts.compilerSettings,
        };
        this._artifactsDir = passedOpts.artifactsDir || config.artifactsDir || DEFAULT_ARTIFACTS_DIR;
        this._specifiedContracts = passedOpts.contracts || config.contracts || ALL_CONTRACTS_IDENTIFIER;
        this._useDockerisedSolc =
            passedOpts.useDockerisedSolc || config.useDockerisedSolc || DEFAULT_USE_DOCKERISED_SOLC;
        this._isOfflineMode = passedOpts.isOfflineMode || config.isOfflineMode || DEFAULT_IS_OFFLINE_MODE;
        this._shouldSaveStandardInput =
            passedOpts.shouldSaveStandardInput || config.shouldSaveStandardInput || DEFAULT_SHOULD_SAVE_STANDARD_INPUT;
        this._nameResolver = new NameResolver(this._contractsDir);
        const resolver = new FallthroughResolver();
        resolver.appendResolver(new URLResolver());
        resolver.appendResolver(new NPMResolver(this._contractsDir));
        resolver.appendResolver(new RelativeFSResolver(this._contractsDir));
        resolver.appendResolver(new FSResolver());
        resolver.appendResolver(this._nameResolver);
        this._resolver = resolver;
    }
    /**