handleReadExtensions_(features) {
    if (!features) {
      features = [];
    }
    for (let i = 0, ii = features.length; i < ii; ++i) {
      const feature = features[i];
      if (this.readExtensions_) {
        const extensionsNode = feature.get('extensionsNode_') || null;
        this.readExtensions_(feature, extensionsNode);
      }
      feature.set('extensionsNode_', undefined);
    }
  }
@param {Array<Feature>} features List of features.
@private