addBatch(intent, entities) {
    const result = [];
    if (entities && entities.length > 0) {
      entities.forEach((entity) => {
        let slot = this.getSlot(intent, entity);
        if (!slot) {
          slot = this.addSlot(intent, entity);
        }
        result.push(slot);
      });
    }
    return result;
  }
Add several entities if they don't exists.
@param {String} intent Name of the intent.
@param {String[]} entities List of entities.
@returns {Object[]} Array of resulting entities.