Die Definition der Typen war nicht ausreichend.

.gitignore

@@ -105,3 +105,4 @@ Temporary Items
 /api/vendor/
 /api/tests/_*
 /api/tests/*.suite.yml
+/api/.env

api/.env

@@ -1,5 +0,0 @@
-## Datenbank-Einstellungen
-DATABASES_HOST=psql.torsten-hettstedt.net
-DATABASES_NAME=torsten
-DATABASES_USER=web_user
-DATABASES_PASS=V6ZGhtdXEbxH8oWD

api/.env.example

@@ -0,0 +1,5 @@
+## Datenbank-Einstellungen
+DATABASES_HOST=psql.domain.tld
+DATABASES_NAME=db
+DATABASES_USER=user
+DATABASES_PASS=1234

api/Dockerfile

@@ -1,6 +1,5 @@
 FROM php:8.0-apache
 
-#RUN apt update && apt install -y postgresql postgresql-client
 RUN apt update && apt install -y libpq-dev
 RUN docker-php-ext-install -j$(nproc) pdo pdo_pgsql
 

api/src/Controller/HttpConflictRequestException.php

@@ -6,16 +6,15 @@ use Slim\Exception\HttpSpecializedException;
 
 class HttpConflictRequestException extends HttpSpecializedException
 {
-    /**
-     * @var int
-     */
+    /** @var int */
     protected $code = 409;
 
-    /**
-     * @var string
-     */
+    /** @var string */
     protected $message = 'Conflict.';
 
+    /** @var string  */
     protected $title = '409 Conflict';
+
+    /** @var string  */
     protected $description = 'The 409 (Conflict) status code indicates that the request could not be completed due to a conflict with the current state of the target resource.';
 }