Problem with PHP version 8.1

[Noel da Costa]

I upgraded to PHP version 8.1 recently and as a result I'm now getting all of these warnings.

2023-01-27 19:52:18 warning: Cannot modify header information - headers already sent by (output started at /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Error/Renderer/HtmlErrorRenderer.php:36)
Request URL: /api/notarials
Referer URL: https://fe.mnr.localhost/
Client IP: 172.21.0.1
Trace:
header [internal], line ??
Cake\Http\ResponseEmitter::emitHeaders() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 197
Cake\Http\ResponseEmitter::emit() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 75
Cake\Http\Server::emit() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Server.php, line 128
[main] /var/www/html/crud-json-example/webroot/index.php, line 40
2023-01-27 19:52:18 notice: Return type of Neomerx\JsonApi\Schema\ErrorCollection::offsetUnset($offset) should either be compatible with ArrayAccess::offsetUnset(mixed $offset): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice
Request URL: /api/notarials
Referer URL: https://fe.mnr.localhost/
Client IP: 172.21.0.1
Trace:
include /var/www/html/crud-json-example/vendor/neomerx/json-api/src/Schema/ErrorCollection.php, line 36
Composer\Autoload\includeFile /var/www/html/crud-json-example/vendor/composer/ClassLoader.php, line 571
Composer\Autoload\ClassLoader::loadClass() /var/www/html/crud-json-example/vendor/composer/ClassLoader.php, line 428
CrudJsonApi\Listener\JsonApi\DocumentValidator::__construct() /var/www/html/crud-json-example/vendor/friendsofcake/crud-json-api/src/Listener/JsonApi/DocumentValidator.php, line 58
CrudJsonApi\Listener\JsonApiListener::_checkRequestData() /var/www/html/crud-json-example/vendor/friendsofcake/crud-json-api/src/Listener/JsonApiListener.php, line 1264
CrudJsonApi\Listener\JsonApiListener::beforeHandle() /var/www/html/crud-json-example/vendor/friendsofcake/crud-json-api/src/Listener/JsonApiListener.php, line 131
Cake\Event\EventManager::_callListener() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Event/EventManager.php, line 309
Cake\Event\EventManager::dispatch() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Event/EventManager.php, line 286
Crud\Controller\Component\CrudComponent::trigger() /var/www/html/crud-json-example/vendor/friendsofcake/crud/src/Controller/Component/CrudComponent.php, line 550
Crud\Controller\Component\CrudComponent::execute() /var/www/html/crud-json-example/vendor/friendsofcake/crud/src/Controller/Component/CrudComponent.php, line 242
App\Controller\Baked\NotarialsController::add() /var/www/html/crud-json-example/src/Controller/Baked/NotarialsController.php, line 63
App\Controller\Api\NotarialsController::add() /var/www/html/crud-json-example/src/Controller/Api/NotarialsController.php, line 21
Cake\Controller\Controller::invokeAction() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Controller/Controller.php, line 547
App\Controller\AppController::invokeAction() /var/www/html/crud-json-example/vendor/friendsofcake/crud/src/Controller/ControllerTrait.php, line 80
Cake\Controller\ControllerFactory::handle() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Controller/ControllerFactory.php, line 139
Cake\Controller\ControllerFactory::invoke() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Controller/ControllerFactory.php, line 114
Cake\Http\BaseApplication::handle() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/BaseApplication.php, line 320
Cake\Http\Runner::handle() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Runner.php, line 77
Authorization\Middleware\RequestAuthorizationMiddleware::process() /var/www/html/crud-json-example/vendor/cakephp/authorization/src/Middleware/RequestAuthorizationMiddleware.php, line 102
Cake\Http\Runner::handle() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Runner.php, line 73
Authorization\Middleware\AuthorizationMiddleware::process() /var/www/html/crud-json-example/vendor/cakephp/authorization/src/Middleware/AuthorizationMiddleware.php, line 129
Cake\Http\Runner::handle() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Runner.php, line 73
Authentication\Middleware\AuthenticationMiddleware::process() /var/www/html/crud-json-example/vendor/cakephp/authentication/src/Middleware/AuthenticationMiddleware.php, line 124
Cake\Http\Runner::handle() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Runner.php, line 73
Cake\Http\Runner::handle() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Runner.php, line 77
Cake\Http\Middleware\BodyParserMiddleware::process() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Middleware/BodyParserMiddleware.php, line 172
Cake\Http\Runner::handle() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Runner.php, line 73
Cors\Middleware\CorsMiddleware::process() /var/www/html/crud-json-example/plugins/Cors/src/Middleware/CorsMiddleware.php, line 26
Cake\Http\Runner::handle() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Runner.php, line 73
Cake\Http\Runner::run() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Runner.php, line 58
Cake\Routing\Middleware\RoutingMiddleware::process() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Routing/Middleware/RoutingMiddleware.php, line 192
Cake\Http\Runner::handle() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Runner.php, line 73
Cake\Routing\Middleware\AssetMiddleware::process() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Routing/Middleware/AssetMiddleware.php, line 68
Cake\Http\Runner::handle() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Runner.php, line 73
Cake\Error\Middleware\ErrorHandlerMiddleware::process() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Error/Middleware/ErrorHandlerMiddleware.php, line 131
Cake\Http\Runner::handle() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Runner.php, line 73
Cake\Http\Runner::run() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Runner.php, line 58
Cake\Http\Server::run() /var/www/html/crud-json-example/vendor/cakephp/cakephp/src/Http/Server.php, line 90
[main] /var/www/html/crud-json-example/webroot/index.php, line 40