FIX return type of return by adding null in return (#28503)

htdocs/core/class/lessc.class.php

@@ -2281,7 +2281,7 @@ class Lessc
 	 *
 	 * @param mixed $in Input
 	 * @param bool $force Force rebuild?
-	 * @return array lessphp cache structure
+	 * @return array|null lessphp cache structure
 	 */
 	public function cachedCompile($in, $force = false)
 	{