Metatag "news_keywords" for Blogger

As you know Google announced new meta tag "news_keywords".

I'm trying to create a code that would generate the content of the meta tag "news_keywords" in Google Blogger.

I think that this can be implemented using the labels.

While there is a version of the code but it does not work.

Code:

---

<b:if cond='data:blog.pageType == &quot;item&quot;'>
&lt;meta name=&quot;news_keywords&quot; content=&quot;<b:loop values='data:post.labels' var='label'><data:label.name/><b:if cond='data:label.isLast != &quot;true&quot;'>, </b:if></b:loop>&quot;/&gt;
</b:if>

---

Paste this code into template your blog on Blogger. Open the source code of the post which has a label.
If you look in the code source of the page we see the construction of a meta tag:

Code:

---

<meta name="news_keywords" content="TEMPLATE ERROR: No dictionary named: 'post' in: ['blog', 'skin', 'view']"/>

---

Could you help me finish the code?

You can open the source code of the page of my blog use CTRL-F and you will find the meta tag "news_keywords".

While this meta-tag is displayed in the < body > only. This is not correct, but in < head > it does not work.