calendar-bundle/src/Resources/contao/modules/ModuleCalendar.php
public function generate()
	{
		if (TL_MODE == 'BE')
		{
			$objTemplate = new BackendTemplate('be_wildcard');
			$objTemplate->wildcard = '### ' . Utf8::strtoupper($GLOBALS['TL_LANG']['FMD']['calendar'][0]) . ' ###';
			$objTemplate->title = $this->headline;
			$objTemplate->id = $this->id;
			$objTemplate->link = $this->name;
			$objTemplate->href = 'contao/main.php?do=themes&amp;table=tl_module&amp;act=edit&amp;id=' . $this->id;

			return $objTemplate->parse();
		}

		$this->cal_calendar = $this->sortOutProtected(StringUtil::deserialize($this->cal_calendar, true));

		// Return if there are no calendars
		if (empty($this->cal_calendar) || !\is_array($this->cal_calendar))
		{
			return '';
		}

		$this->strUrl = preg_replace('/\?.*$/', '', Environment::get('request'));
		$this->strLink = $this->strUrl;

		if (($objTarget = $this->objModel->getRelated('jumpTo')) instanceof PageModel)
		{
			/** @var PageModel $objTarget */
			$this->strLink = $objTarget->getFrontendUrl();
		}

		return parent::generate();
	}
public function generate()
	{
		if (TL_MODE == 'BE')
		{
			$objTemplate = new BackendTemplate('be_wildcard');
			$objTemplate->wildcard = '### ' . Utf8::strtoupper($GLOBALS['TL_LANG']['FMD']['calendar'][0]) . ' ###';
			$objTemplate->title = $this->headline;
			$objTemplate->id = $this->id;
			$objTemplate->link = $this->name;
			$objTemplate->href = 'contao/main.php?do=themes&amp;table=tl_module&amp;act=edit&amp;id=' . $this->id;

			return $objTemplate->parse();
		}

		$this->cal_calendar = $this->sortOutProtected(StringUtil::deserialize($this->cal_calendar, true));

		// Return if there are no calendars
		if (empty($this->cal_calendar) || !\is_array($this->cal_calendar))
		{
			return '';
		}

		$this->strUrl = preg_replace('/\?.*$/', '', Environment::get('request'));
		$this->strLink = $this->strUrl;

		if (($objTarget = $this->objModel->getRelated('jumpTo')) instanceof PageModel)
		{
			/** @var PageModel $objTarget */
			$this->strLink = $objTarget->getFrontendUrl();
		}

		return parent::generate();
	}
Do not show the module if no calendar has been selected

@return string