[BUG]: Phalcon\Crypt::getKey may return null

[sergeyklay]

The current implementation of Phalcon\Crypt::getKey implies that method must return string:

cphalcon/phalcon/Crypt.zep

Lines 427 to 430 in 3049c86

	public function getKey() -> string
	{
	return this->key;
	}

however, Phalcon\Crypt::$key is NULL by default:

cphalcon/phalcon/Crypt.zep

Lines 57 to 60 in 3049c86

	/**
	* @var string
	*/
	protected key;

This leads to a fatal error:

$crypt = new \Phalcon\Crypt();
$crypt->getKey();

PHP Fatal error:
Return value of Phalcon\Crypt::getKey()
must be of the type string, null returned

[sergeyklay]

Fixed in 4.0.x branch