Yslow is showing undefined value in statistics tab

I need some help to understand what is, or what could be the undefined value that costs 22.7k of Total weight http request in my webpage.
enter image description here
The website is a very basic installation of wordpress in localhost. Here is the source code from "view source" of the tested page:
<!DOCTYPE html>
<html lang="el" class="no-js">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width">
    <link rel="profile" href="http://gmpg.org/xfn/11">
    <link rel="pingback" href="http://localhost/wordpress/xmlrpc.php">
    <!--[if lt IE 9]>
    <script src="http://localhost/wordpress/wp-content/themes/twentyfifteen/js/html5.js"></script>
    <![endif]-->
    <script>(function(html){html.className = html.className.replace(/\bno-js\b/,'js')})(document.documentElement);</script>
<title>wordpress | Just another WordPress site</title>
<link rel="alternate" type="application/rss+xml" title="Κανάλι RSS &raquo; wordpress" href="http://localhost/wordpress/?feed=rss2" />
<link rel="alternate" type="application/rss+xml" title="Κανάλι σχολίων &raquo; wordpress" href="http://localhost/wordpress/?feed=comments-rss2" />
        <script type="text/javascript">
            window._wpemojiSettings = {"baseUrl":"http:\/\/s.w.org\/images\/core\/emoji\/72x72\/","ext":".png","source":{"concatemoji":"http:\/\/localhost\/wordpress\/wp-includes\/js\/wp-emoji-release.min.js?ver=4.2.2"}};
            !function(a,b,c){function d(a){var c=b.createElement("canvas"),d=c.getContext&&c.getContext("2d");return d&&d.fillText?(d.textBaseline="top",d.font="600 32px Arial","flag"===a?(d.fillText(String.fromCharCode(55356,56812,55356,56807),0,0),c.toDataURL().length>3e3):(d.fillText(String.fromCharCode(55357,56835),0,0),0!==d.getImageData(16,16,1,1).data[0])):!1}function e(a){var c=b.createElement("script");c.src=a,c.type="text/javascript",b.getElementsByTagName("head")[0].appendChild(c)}var f,g;c.supports={simple:d("simple"),flag:d("flag")},c.DOMReady=!1,c.readyCallback=function(){c.DOMReady=!0},c.supports.simple&&c.supports.flag||(g=function(){c.readyCallback()},b.addEventListener?(b.addEventListener("DOMContentLoaded",g,!1),a.addEventListener("load",g,!1)):(a.attachEvent("onload",g),b.attachEvent("onreadystatechange",function(){"complete"===b.readyState&&c.readyCallback()})),f=c.source||{},f.concatemoji?e(f.concatemoji):f.wpemoji&&f.twemoji&&(e(f.twemoji),e(f.wpemoji)))}(window,document,window._wpemojiSettings);
        </script>
        <style type="text/css">
img.wp-smiley,
img.emoji {
    display: inline !important;
    border: none !important;
    box-shadow: none !important;
    height: 1em !important;
    width: 1em !important;
    margin: 0 .07em !important;
    vertical-align: -0.1em !important;
    background: none !important;
    padding: 0 !important;
}
</style>
<link rel='stylesheet' id='twentyfifteen-fonts-css'  href='//fonts.googleapis.com/css?family=Noto+Sans%3A400italic%2C700italic%2C400%2C700%7CNoto+Serif%3A400italic%2C700italic%2C400%2C700%7CInconsolata%3A400%2C700&#038;subset=latin%2Clatin-ext' type='text/css' media='all' />
<link rel='stylesheet' id='genericons-css'  href='http://localhost/wordpress/wp-content/themes/twentyfifteen/genericons/genericons.css?ver=3.2' type='text/css' media='all' />
<link rel='stylesheet' id='twentyfifteen-style-css'  href='http://localhost/wordpress/wp-content/themes/twentyfifteen/style.css?ver=4.2.2' type='text/css' media='all' />
<!--[if lt IE 9]>
<link rel='stylesheet' id='twentyfifteen-ie-css'  href='http://localhost/wordpress/wp-content/themes/twentyfifteen/css/ie.css?ver=20141010' type='text/css' media='all' />
<![endif]-->
<!--[if lt IE 8]>
<link rel='stylesheet' id='twentyfifteen-ie7-css'  href='http://localhost/wordpress/wp-content/themes/twentyfifteen/css/ie7.css?ver=20141010' type='text/css' media='all' />
<![endif]-->
<script type='text/javascript' src='http://localhost/wordpress/wp-includes/js/jquery/jquery.js?ver=1.11.2'></script>
<script type='text/javascript' src='http://localhost/wordpress/wp-includes/js/jquery/jquery-migrate.min.js?ver=1.2.1'></script>
<link rel="EditURI" type="application/rsd+xml" title="RSD" href="http://localhost/wordpress/xmlrpc.php?rsd" />
<link rel="wlwmanifest" type="application/wlwmanifest+xml" href="http://localhost/wordpress/wp-includes/wlwmanifest.xml" /> 
<meta name="generator" content="WordPress 4.2.2" />
    <style type="text/css">.recentcomments a{display:inline !important;padding:0 !important;margin:0 !important;}</style>
</head>

<body class="home blog">
<div id="page" class="hfeed site">
    <a class="skip-link screen-reader-text" href="#content">Μετάβαση σε περιεχόμενο</a>

    <div id="sidebar" class="sidebar">
        <header id="masthead" class="site-header" role="banner">
            <div class="site-branding">
                                        <h1 class="site-title"><a href="http://localhost/wordpress/" rel="home">wordpress</a></h1>
                                            <p class="site-description">Just another WordPress site</p>
                                    <button class="secondary-toggle">Μενού και μονάδες</button>
            </div><!-- .site-branding -->
        </header><!-- .site-header -->

            <div id="secondary" class="secondary">

                    <div id="widget-area" class="widget-area" role="complementary">
                <aside id="search-2" class="widget widget_search"><form role="search" method="get" class="search-form" action="http://localhost/wordpress/">
                <label>
                    <span class="screen-reader-text">Αναζήτηση για:</span>
                    <input type="search" class="search-field" placeholder="Αναζήτηση&hellip;" value="" name="s" title="Αναζήτηση για:" />
                </label>
                <input type="submit" class="search-submit screen-reader-text" value="Αναζήτηση" />
            </form></aside>     <aside id="recent-posts-2" class="widget widget_recent_entries">        <h2 class="widget-title">Πρόσφατα άρθρα</h2>       <ul>
                    <li>
                <a href="http://localhost/wordpress/?p=1">Hello world!</a>
                        </li>
                </ul>
        </aside><aside id="recent-comments-2" class="widget widget_recent_comments"><h2 class="widget-title">Πρόσφατα σχόλια</h2><ul id="recentcomments"><li class="recentcomments"><span class="comment-author-link"><a href='https://wordpress.org/' rel='external nofollow' class='url'>Mr WordPress</a></span> στη <a href="http://localhost/wordpress/?p=1#comment-1">Hello world!</a></li></ul></aside><aside id="archives-2" class="widget widget_archive"><h2 class="widget-title">Αρχείο</h2>       <ul>
    <li><a href='http://localhost/wordpress/?m=201501'>Ιανουαρίου 2015</a></li>
        </ul>
</aside><aside id="categories-2" class="widget widget_categories"><h2 class="widget-title">Kατηγορίες</h2>     <ul>
    <li class="cat-item cat-item-1"><a href="http://localhost/wordpress/?cat=1" >Uncategorized</a>
</li>
        </ul>
</aside><aside id="meta-2" class="widget widget_meta"><h2 class="widget-title">Μεταστοιχεία</h2>            <ul>
                        <li><a href="http://localhost/wordpress/wp-login.php">Σύνδεση</a></li>
            <li><a href="http://localhost/wordpress/?feed=rss2">Κανάλι <abbr title="Really Simple Syndication">RSS</abbr> άρθρων</a></li>
            <li><a href="http://localhost/wordpress/?feed=comments-rss2">Κανάλι <abbr title="Really Simple Syndication">RSS</abbr> σχολίων</a></li>
<li><a href="https://wordpress.org/" title="Κατασκευασμένο με WordPress, το προηγμένο σύστημα ιστοδημοσιεύσεων.">WordPress.org</a></li>           </ul>
</aside>            </div><!-- .widget-area -->

    </div><!-- .secondary -->

    </div><!-- .sidebar -->

    <div id="content" class="site-content">

    <div id="primary" class="content-area">
        <main id="main" class="site-main" role="main">

<article id="post-1" class="post-1 post type-post status-publish format-standard hentry category-uncategorized">

    <header class="entry-header">
        <h2 class="entry-title"><a href="http://localhost/wordpress/?p=1" rel="bookmark">Hello world!</a></h2>  </header><!-- .entry-header -->

    <div class="entry-content">
        <p>Welcome to WordPress. This is your first post. Edit or delete it, then start blogging!</p>
    </div><!-- .entry-content -->

    <footer class="entry-footer">
        <span class="posted-on"><span class="screen-reader-text">Δημοσιεύτηκε την </span><a href="http://localhost/wordpress/?p=1" rel="bookmark"><time class="entry-date published updated" datetime="2015-01-14T18:57:10+00:00">Ιανουαρίου 14, 2015</time></a></span><span class="comments-link"><a href="http://localhost/wordpress/?p=1#comments">1 Σχόλιο</a></span>            </footer><!-- .entry-footer -->

</article><!-- #post-## -->

        </main><!-- .site-main -->
    </div><!-- .content-area -->

    </div><!-- .site-content -->

    <footer id="colophon" class="site-footer" role="contentinfo">
        <div class="site-info">
                        <a href="https://wordpress.org/">Κατασκευασμένο με WordPress</a>
        </div><!-- .site-info -->
    </footer><!-- .site-footer -->

</div><!-- .site -->

<script type='text/javascript' src='http://localhost/wordpress/wp-content/themes/twentyfifteen/js/skip-link-focus-fix.js?ver=20141010'></script>
<script type='text/javascript'>
/* <![CDATA[ */
var screenReaderText = {"expand":"<span class=\"screen-reader-text\">\u03b5\u03c0\u03ad\u03ba\u03c4\u03b1\u03c3\u03b7 \u03c4\u03bf\u03c5 \u03bc\u03b5\u03bd\u03bf\u03cd \u03b1\u03c0\u03cc\u03b3\u03bf\u03bd\u03bf\u03c2<\/span>","collapse":"<span class=\"screen-reader-text\">\u03ac\u03bd\u03bf\u03b9\u03b3\u03bc\u03b1 \u03c5\u03c0\u03cc-\u03bc\u03b5\u03bd\u03bf\u03cd<\/span>"};
/* ]]> */
</script>
<script type='text/javascript' src='http://localhost/wordpress/wp-content/themes/twentyfifteen/js/functions.js?ver=20150330'></script>

</body>
</html>
marcelduran / yslow

Yslow is showing undefined value in statistics tab #157
