code: public function setDataValidation($pCellCoordinate, DataValidation $pDataValidation = null)
      {
          if ($pDataValidation === null) {
              unset($this->dataValidationCollection[$pCellCoordinate]);
          } else {
              $this->dataValidationCollection[$pCellCoordinate] = $pDataValidation;
          }
  
          return $this;
      }
docs: Set data validation.
  
  @param string $pCellCoordinate Cell coordinate to insert data validation, eg: 'A1'
  @param null|DataValidation $pDataValidation
  
  @return Worksheet