Description:
------------
In PHP FPM, setting listen.allowed_clients to either of the following values will result in PHP-FPM rejecting fastcgi requests

This is unexpected behaviour, as the documentation states that...

(1) If this value is left blank, connections will be accepted from any ip address.

(2) Default Value: any

Test script:
---------------
php-fpm.conf:

[global]
pid = /run/php/php-fpm.pid
error_log = /var/log/php-fpm.log
include=/etc/php-fpm/pool.d/*.conf


pool.d/www.conf (example: 1):

[www]
user = php-fpm
group = php-fpm

listen = 9000
listen.allowed_clients = 


pool.d/www.conf (example: 2):

[www]
user = php-fpm
group = php-fpm

listen = 9000
listen.allowed_clients = any

Expected result:
----------------
Setting listen.allowed_clients to a value of "" or "any" should result in the fastcgi connection being accepted

Actual result:
--------------
PHP-FPM rejects the request, with the following error...

php-fpm_1  | ERROR: Connection disallowed: IP address '172.20.0.5' has been dropped.


Additionally, the following error messages are thrown on startup...

Example 1 (listen.allowed_clients = )

php-fpm_1  | ERROR: Wrong IP address '' in listen.allowed_clients
php-fpm_1  | ERROR: There are no allowed addresses


Example 2 (listen.allowed_clients = any)

php-fpm_1  | ERROR: Wrong IP address 'any' in listen.allowed_clients
php-fpm_1  | ERROR: There are no allowed addresses