How to initialize variable when adding Content Security Policy to Nginx configs?

Question

Nginx

Good afternoon!
After adding the Content Security Policy rules to the Nginx config, errors began to appear in the log file:

2018/12/09 22:55:05 [warn] 500#500: *18 using uninitialized "csp" variable while reading response header from upstream, client: xxx.xx.xx.xxx, server: site.ru, request: "GET /page/2/ HTTP/2.0", upstream: "fastcgi://unix:/var/www/php-fpm/xxxxxxxx.sock:", host: "site.ru", referrer: "https://site.ru/"
2018/12/09 22:55:15 [warn] 500#500: *60 using uninitialized "csp" variable while reading response header from upstream, client: xxx.xx.xx.xxx, server: site.ru, request: "GET /page/2/ HTTP/2.0", upstream: "fastcgi://unix:/var/www/php-fpm/xxxxxxxx.sock:", host: "site.ru", referrer: "https://site.ru/"

Code for adding Content-Security-Policy to /etc/nginx/vhosts-resources/site.ru/general.conf config:

set $CSP_image  "img-src      'self' 'unsafe-inline' 'unsafe-eval' data: *.printfriendly.com *.w.org *.gravatar.com *.vimeocdn.com; ";
set $CSP_script "script-src   'self' 'unsafe-inline' 'unsafe-eval' *.w.org *.gravatar.com *.googleapis.com *.jsdelivr.net *.printfriendly.com *.kxcdn.com *.vimeocdn.com *.hs-analytics.net *.securitymetrics.com *.google-analytics.com; ";
set $CSP_style  "style-src    'self' 'unsafe-inline' *.googleapis.com *.bootstrapcdn.com *.gstatic.com *.vimeocdn.com; ";
set $CSP_font   "font-src     'self' data: *.googleapis.com *.bootstrapcdn.com *.gstatic.com *.googleapis.com; ";
set $CSP_frame  "frame-src    'self' *.vimeocdn.com *.vimeo.com; ";
set $CSP_object "object-src   'self' ; ";
set $CSP        "default-src  'self' ; ${CSP_image} ${CSP_script} ${CSP_style} ${CSP_font} ${CSP_frame} ${CSP_object}";
add_header Content-Security-Policy $CSP;

Why does Nginx consider the $CSP variable to be uninitialized and how to initialize it?
PS Just discovered that the Content Security Policy is given only on the main page, on other pages - no.
PPS Everything, the question is removed - the order of the rules ...