undefined method Minify_Model_CSS::concat()

[aurmil]

set minify.concat_css = true
and minify.minify_css = false
leads to
Fatal error: Call to undefined method Minify_Model_CSS::concat() in /application/modules/minify/controllers/MinifyController.php on line 80

should add

    public static function concat($css, $options = array())
    {
        if (isset($options['preserveComments'])
            && !$options['preserveComments']) {
            $css = Minify_Model_CSS_Compressor::process($css, $options);
        }
        if (! isset($options['currentDir']) && ! isset($options['prependRelativePath'])) {
            return $css;
        }
        if (isset($options['currentDir'])) {
            return Minify_Model_CSS_UriRewriter::rewrite(
                $css
                ,$options['currentDir']
                ,isset($options['docRoot']) ? $options['docRoot'] : $_SERVER['DOCUMENT_ROOT']
                ,isset($options['symlinks']) ? $options['symlinks'] : array()
            );
        } else {
            return Minify_Model_CSS_UriRewriter::prepend(
                $css
                ,$options['prependRelativePath']
            );
        }
    }

in Minify_Model_CSS class