Warning (2) : Undefined variable $user [in /var/www/thimblequilt/src/Controller/ProductdetailController.php, line 102]
Warning (2) : Attempt to read property "id" on null [in /var/www/thimblequilt/src/Controller/ProductdetailController.php, line 102]
Warning (512) : Unable to emit headers. Headers sent in file=/var/www/thimblequilt/vendor/cakephp/cakephp/src/Error/Renderer/HtmlErrorRenderer.php line=37 [in /var/www/thimblequilt/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 71]
Warning (2) : Cannot modify header information - headers already sent by (output started at /var/www/thimblequilt/vendor/cakephp/cakephp/src/Error/Renderer/HtmlErrorRenderer.php:37) [in /var/www/thimblequilt/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 164]
Warning (2) : Cannot modify header information - headers already sent by (output started at /var/www/thimblequilt/vendor/cakephp/cakephp/src/Error/Renderer/HtmlErrorRenderer.php:37) [in /var/www/thimblequilt/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 197]
Error: Expression `user_id` is missing operator (IS, IS NOT) with `null` value.

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

InvalidArgumentException
CORE/src/Database/Expression/QueryExpression.php at line 839 (edit)
            $operator = '!=';
        }
        if ($value === null && $this->_conjunction !== ',') {
            throw new InvalidArgumentException(
                sprintf('Expression `%s` is missing operator (IS, IS NOT) with `null` value.', $expression)
            );
        }

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