Not caching POST request.

I have WP with nginx and this configuration.

set $cache_uri $request_uri;

# POST requests and urls with a query string should always go to PHP
if ($request_method = POST) {
    set $cache_uri 'null cache';
}
if ($query_string != "") {
    set $cache_uri 'null cache';
}

# Don't cache uris containing the following segments
if ($request_uri ~* "(/wp-admin/|/xmlrpc.php|/wp-(app|cron|login|register|mail).php
                      |wp-.*.php|/feed/|index.php|wp-comments-popup.php
                      |wp-links-opml.php|wp-locations.php |sitemap(_index)?.xml
                      |[a-z0-9_-]+-sitemap([0-9]+)?.xml)") {

    set $cache_uri 'null cache';
}

# Don't use the cache for logged-in users or recent commenters
if ($http_cookie ~* "comment_author|wordpress_[a-f0-9]+
                     |wp-postpass|wordpress_logged_in") {
    set $cache_uri 'null cache';
}

# Set the cache file
set $cachefile "/wp-content/cache/supercache/$http_host/$cache_uri/index.html";
if ($https ~* "on") {
    set $cachefile "/wp-content/cache/supercache/$http_host/$cache_uri/index-https.html";
}

# Add cache file debug info as header
#add_header X-Cache-File $cachefile;

# Try in the following order: (1) cachefile, (2) normal url, (3) php
location / {
    try_files $cachefile $uri $uri/ /index.php?$args;
}

All pages end with this:

11:19:40 126068 / wp_cache_get_cookies_values: return: 

11:19:40 126068 / supercache dir: /var/www/clients/client1/web11/web/wp-content/cache/supercache/www.tycico.cz/

11:19:40 126068 / No Super Cache file found for current URL: /var/www/clients/client1/web11/web/wp-content/cache/supercache/www.tycico.cz/index-https.html

11:19:40 126068 / wp_cache_get_cookies_values: return: 

11:19:40 126068 / In WP Cache Phase 2

11:19:40 126068 / Setting up WordPress actions

11:19:40 126068 / Created output buffer

11:19:41 126068 / Not caching POST request.

11:19:41 126068 / wp_cache_maybe_dynamic: returned $buffer

No pages are cached. What could be wrong?

Thanks for reply.