What exactly is returned by ini_get in that case? An empty string or null?
Because looking at the existing checks and its comments it seems to be important to not use a generic boolean like empty here. If you check here using empty, the previous check which explicitely checks for an integer 0 would be not needed anymore. empty will return true for a boolean false, an integer 0, an empty string or a string containing 0 and for null.

What exactly is returned by ini_get in that case? An empty string or null?

Can you answer here @anibalsanchez ?

I only create the patch based on the comment by @anibalsanchez on the JC Tracker.

Same issue here!
In PHP Information tab: xcache.admin.enable_auth=Off
ini_get('xcache.admin.enable_auth') is empty
Confirmed in PHP 5.5.3 and 5.3.10.

Quick fix, xcache.php, line 238, return true; ... or check for empty $xcache_admin_enable_auth a couple of lines below.

        if (extension_loaded('xcache'))
        {
            // XCache Admin must be disabled for Joomla to use XCache
            $xcache_admin_enable_auth = ini_get('xcache.admin.enable_auth');

isset($xcache_admin_enable_auth) => true
empty($xcache_admin_enable_auth) => true
is_null($xcache_admin_enable_auth) => false

($xcache_admin_enable_auth === '0') => false
($xcache_admin_enable_auth == '0') => false
($xcache_admin_enable_auth === '') => true
($xcache_admin_enable_auth == '') => true

@test Patch works Ok! Txs!

($xcache_admin_enable_auth === '') => true

Looks like it's an empty string then. I'd suggest to use this as the check instead of empty which may be to generic.

done @Bakual with zero-24@6a2e70a

Looks good to me. @anibalsanchez can you please test this latest version again?

It works perfect! I've already deployed to it several sites.

thanks @anibalsanchez and @Bakual