How to use the verror.WError.apply function in verror

function SigningError(cause) {
    this.code = 'SigningError';
    assert.optionalObject(cause);
    var msg = 'error signing request';
    var args = (cause ? [cause, msg] : [msg]);
    WError.apply(this, args);
}
util.inherits(SigningError, WError);

function CmdlnError(options) {
    assert.object(options, 'options');
    assert.string(options.message, 'options.message');
    assert.optionalString(options.code, 'options.code');
    if (!options.code) options.code = 'Cmdln';
    assert.optionalObject(options.cause, 'options.cause');
    var self = this;

    var args = [];
    if (options.cause) args.push(options.cause);
    args.push(options.message);
    WError.apply(this, args);

    var extra = Object.keys(options).filter(
        function (k) { return ['cause', 'message'].indexOf(k) === -1; });
    extra.forEach(function (k) {
        self[k] = options[k];
    });
}
util.inherits(CmdlnError, WError);

function HttpError(options) {
    assert.object(options, 'options');

    options.constructorOpt = options.constructorOpt || HttpError;
    WError.apply(this, arguments);

    var self = this;
    var code = parseInt((options.statusCode || 500), 10);
    this.statusCode = code;
    this.body = options.body || {
        code: codeToErrorName(code),
        message: options.message || self.message
    };
    this.message = options.message || self.message;
}
util.inherits(HttpError, WError);

function HttpError(options) {
        assert.object(options, 'options');

        options.constructorOpt = options.constructorOpt || HttpError;
        WError.apply(this, arguments);
        this.name = this.constructor.name;

        var self = this;
        var code = parseInt((options.statusCode || 500), 10);
        this.statusCode = code;
        this.body = options.body || {
                code: codeToErrorName(code),
                message: options.message || self.message
        };
        this.message = options.message || self.message;
}
util.inherits(HttpError, WError);

function ChecksumError(cause, actual, expected) {
    this.code = 'ChecksumError';
    if (expected === undefined) {
        expected = actual;
        actual = cause;
        cause = undefined;
    }
    assert.optionalObject(cause);
    assert.string(actual);
    assert.string(expected);

    var args = [];
    if (cause) args.push(cause);
    args = args.concat('content-md5 expected to be %s, but was %s',
        expected, actual);
    WError.apply(this, args);
}
util.inherits(ChecksumError, WError);

function CmdlnError(options) {
    assert.object(options, 'options');
    assert.string(options.message, 'options.message');
    assert.optionalString(options.code, 'options.code');
    if (!options.code) options.code = 'Cmdln';
    assert.optionalObject(options.cause, 'options.cause');
    var self = this;

    var args = [];
    if (options.cause) args.push(options.cause);
    args.push(options.message);
    WError.apply(this, args);

    var extra = Object.keys(options).filter(
        function (k) { return ['cause', 'message'].indexOf(k) === -1; });
    extra.forEach(function (k) {
        self[k] = options[k];
    });
}
util.inherits(CmdlnError, WError);