code: public Optional<AlertCondition> add(long entityId, String entityType, long conditionId)
      {
          QueryParameterList queryParams = new QueryParameterList();
          queryParams.add("entity_type", entityType);
          queryParams.add("condition_id", conditionId);
          return HTTP.PUT(String.format("/v2/alerts_entity_conditions/%d.json", entityId), null, null, queryParams, ALERT_CONDITION);
      }
docs: Adds the given entity to the alert condition with the given id.
  @param entityId The id of the entity to add
  @param entityType The type of the entity to add
  @param conditionId The id of the alert condition to add the entity to
  @return The alert condition that was updated