Deprecated function: str_starts_with(): Passing null to parameter #1 ($haystack) of type string is deprecated

Thanks for reporting.

Will need steps to reproduce.

Also would need to investigate why \Drupal::routeMatch()->getRouteName() is returning null. Could be masking a larger problem.

Tried to reproduce this but didn't face any issue

IHello,

I get same:
Error message
Deprecated function: str_starts_with(): Passing null to parameter #1 ($haystack) of type string is deprecated in Drupal\Core\Routing\UrlGenerator->generateFromRoute() (line 309 of core/lib/Drupal/Core/Routing/UrlGenerator.php).

with :
# Linux config
$ hostnamectl
Static hostname: deb-win
Icon name: computer-desktop
Chassis: desktop 🖥️
Machine ID: fafc07d395216ad0c3eee845473b7092
Boot ID: a3e1cd31b982e29df762
Operating System: Debian GNU/Linux 12 (bookworm)
Kernel: Linux 6.1.0-27-amd64
Architecture: x86-64
Hardware Vendor: Dell Inc.
Hardware Model: Precision Tower 5810
Firmware Version: A20
$ cat /etc/issue
Debian GNU/Linux 12 \n \l

$ cat /etc/os-release
PRETTY_NAME="Debian GNU/Linux 12 (bookworm)"
NAME="Debian GNU/Linux"
VERSION_ID="12"
VERSION="12 (bookworm)"
VERSION_CODENAME=bookworm
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"
$ lsb_release -crid
No LSB modules are available.
Distributor ID: Debian
Description: Debian GNU/Linux 12 (bookworm)
Release: 12
Codename: bookworm

# Drupal config
$ drush core-status
Drupal version : 10.3.10
Site URI : http://default
DB driver : mysql
DB hostname : localhost
DB port : 3306
DB username : toomuch
DB name : babxyz
Database : Connected
Drupal bootstrap : Successful
Default theme : olivero
Admin theme : claro
PHP binary : /usr/bin/php8.2
PHP config : /etc/php/8.2/cli/php.ini
PHP OS : Linux
PHP version : 8.2.25
Drush script : /home/bertrand/projects/babxyz/vendor/bin/drush.php
Drush version : 13.3.2.0
Drush temp : /tmp
Drush configs : /home/bertrand/.drush/drush.yml
/home/bertrand/projects/babxyz/vendor/drush/drush/drush.yml
Install profile : standard
Drupal root : /home/bertrand/projects/babxyz/web
Site path : sites/default
Files, Public : sites/default/files/public
Files, Private : sites/default/files/private
Files, Temp : /tmp

Bertrand

I observed this on a site, and found my way to this issue.

On the affected site, the return value of $route_name = \Drupal::routeMatch()->getRouteName(); on the 404 page was NULL when this happened.

Cross-checking on a different site, I saw that the route on a 404 page is system.404.

I observed that on the affected site, the stack trace originated from BigPipe. When BigPipe module was disabled on the affected site, I was unable to reproduce the issue.