code: protected function normalizeSelect()
      {
          if ($this->fieldsMustBeSelected()) {
              $this->select = array_merge($this->standardFields, $this->select);
          }
  
          if ($this->propsMustBeSelected()) {
              $this->select[] = 'IBLOCK_ID';
              $this->select[] = 'UF_*';
          }
  
          $this->select[] = 'ID';
  
          return $this->clearSelectArray();
      }
docs: Normalize select before sending it to getList.
  This prevents some inconsistency.
  
  @return array