Warning (2) : Trying to access array offset on null [in /home/klient.dhosting.pl/mango/kino.ngo.com.pl/public_html/src/Controller/Front/PagesController.php, line 119]
Warning (512) : Unable to emit headers. Headers sent in file=/home/klient.dhosting.pl/mango/kino.ngo.com.pl/public_html/vendor/cakephp/cakephp/src/Error/Renderer/HtmlErrorRenderer.php line=37 [in /home/klient.dhosting.pl/mango/kino.ngo.com.pl/public_html/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 65]
Warning (2) : Cannot modify header information - headers already sent by (output started at /home/klient.dhosting.pl/mango/kino.ngo.com.pl/public_html/vendor/cakephp/cakephp/src/Error/Renderer/HtmlErrorRenderer.php:37) [in /home/klient.dhosting.pl/mango/kino.ngo.com.pl/public_html/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 159]
Warning (2) : Cannot modify header information - headers already sent by (output started at /home/klient.dhosting.pl/mango/kino.ngo.com.pl/public_html/vendor/cakephp/cakephp/src/Error/Renderer/HtmlErrorRenderer.php:37) [in /home/klient.dhosting.pl/mango/kino.ngo.com.pl/public_html/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 192]
Error: Expression `category_id` is missing operator (IS, IS NOT) with `null` value.

Expression `category_id` is missing operator (IS, IS NOT) with `null` value. 📋

InvalidArgumentException
CORE/src/Database/Expression/QueryExpression.php at line 747 (edit)
<?php             $operator = '!=';
<?php         }
<?php 
<?php         if ($value === null && $this->_conjunction !== ',') {
<?php             throw new InvalidArgumentException(
<?php                 sprintf('Expression `%s` is missing operator (IS, IS NOT) with `null` value.', $expression)
<?php             );
<?php         }
<?php 

If you want to customize this error message, create templates/Error/error500.php