core-bundle/src/Resources/contao/library/Contao/Widget.php
public function getEmptyStringOrNull()
	{
		if (!isset($GLOBALS['TL_DCA'][$this->strTable]['fields'][$this->strField]['sql']))
		{
			return '';
		}

		return static::getEmptyStringOrNullByFieldType($GLOBALS['TL_DCA'][$this->strTable]['fields'][$this->strField]['sql']);
	}
public function getEmptyStringOrNull()
	{
		if (!isset($GLOBALS['TL_DCA'][$this->strTable]['fields'][$this->strField]['sql']))
		{
			return '';
		}

		return static::getEmptyStringOrNullByFieldType($GLOBALS['TL_DCA'][$this->strTable]['fields'][$this->strField]['sql']);
	}
Return either an empty string or null based on the SQL string

@return string|int|null The empty value