using array_key_exists() instead of isset() - required because in case the value is null isset is returning false

lib/private/appconfig.php

@@ -147,7 +147,7 @@ class AppConfig implements \OCP\IAppConfig {
 	 */
 	public function hasKey($app, $key) {
 		$values = $this->getAppValues($app);
-		return isset($values[$key]);
+		return array_key_exists($key, $values);
 	}
 
 	/**