core-bundle/src/Resources/contao/library/Contao/Model/Collection.php
public function __isset($strKey)
	{
		if ($this->intIndex < 0)
		{
			$this->first();
		}

		return isset($this->arrModels[$this->intIndex]->$strKey);
	}
public function __isset($strKey)
	{
		if ($this->intIndex < 0)
		{
			$this->first();
		}

		return isset($this->arrModels[$this->intIndex]->$strKey);
	}
Check whether a property is set

@param string $strKey The property name

@return boolean True if the property is set