code: public function setDateTimeValue($value = null)
      {
          if ($value != null && !$value instanceof \DateTime) {
              throw new \InvalidArgumentException('Expected a \DateTime object.');
          }
  
          $this->type = Cell::TIMESTAMP_TYPE;
          $this->value = $value->getTimestamp();
  
          return $this;
      }
docs: @param \DateTime $value
  
  @return $this