ImportProcessor: The previews-directory set in the constructor is mar…

…ked as optional because it should only be used by internal calls. Added PHP-Doc for the constructor.

min/lib/Minify/ImportProcessor.php

@@ -41,7 +41,11 @@ public static function process($file)
 
     private static $_isCss = null;
 
-    private function __construct($currentDir, $previewsDir)
+    /**
+     * @param String $currentDir
+     * @param String $previewsDir Is only used internally
+     */
+    private function __construct($currentDir, $previewsDir = "")
     {
         $this->_currentDir = $currentDir;
         $this->_previewsDir = $previewsDir;