_fixEntitiesField(obj) {
    const entities = obj.entities;
    const captionEntities = obj.caption_entities;
    const explanationEntities = obj.explanation_entities;
    if (entities && typeof entities !== 'string') {
      obj.entities = stringify(entities);
    }

    if (captionEntities && typeof captionEntities !== 'string') {
      obj.caption_entities = stringify(captionEntities);
    }

    if (explanationEntities && typeof explanationEntities !== 'string') {
      obj.explanation_entities = stringify(explanationEntities);
    }
  }
Fix 'entities' or 'caption_entities' or 'explanation_entities' parameter by making it JSON-serialized, as
required by the Telegram Bot API
@param {Object} obj Object;
@private
@see https://core.telegram.org/bots/api#sendmessage
@see https://core.telegram.org/bots/api#copymessage
@see https://core.telegram.org/bots/api#sendpoll