How to use the eslint/lib/config/config-ops.merge function in eslint

upgrade(originalConfig) {
    if (typeof originalConfig === "undefined" || originalConfig === null) {
      return {};
    }

    let config = merge({}, originalConfig);

    this._report = [];

    let report = upgradeEcmaFeatures(config);
    this._report = this._report.concat(report);
    if (Reflect.has(config, "rules")) {
      report = upgradeRules(config.rules);
      this._report = this._report.concat(report);
    }

    return config;
  }

filter(originalConfig) {
    if (typeof originalConfig === "undefined" || originalConfig === null) {
      return {};
    }

    let config = merge({}, originalConfig);

    this._report = [];

    if (Reflect.has(config, "rules")) {
      let report = filterRules(config.rules);
      this._report = this._report.concat(report);
    }

    return config;
  }

mergeConfig(prev: Object, next: Object): Object {
    return ConfigOps.merge(prev, next);
  }
}