fix: IriConverter does not return null anywhere

Author: rvanlaak

src/Laravel/Routing/IriConverter.php

@@ -91,7 +91,7 @@ public function getResourceFromIri(string $iri, array $context = [], ?Operation
     /**
      * @param array<string, mixed> $context
      */
-    public function getIriFromResource(object|string $resource, int $referenceType = UrlGeneratorInterface::ABS_PATH, ?Operation $operation = null, array $context = []): ?string
+    public function getIriFromResource(object|string $resource, int $referenceType = UrlGeneratorInterface::ABS_PATH, ?Operation $operation = null, array $context = []): string
     {
         $resourceClass = $context['force_resource_class'] ?? (\is_string($resource) ? $resource : $this->getObjectClass($resource));
         if ($resource instanceof Relation) {

src/Metadata/IriConverterInterface.php

@@ -45,5 +45,5 @@ public function getResourceFromIri(string $iri, array $context = [], ?Operation
      * @throws InvalidArgumentException
      * @throws RuntimeException
      */
-    public function getIriFromResource(object|string $resource, int $referenceType = UrlGeneratorInterface::ABS_PATH, ?Operation $operation = null, array $context = []): ?string;
+    public function getIriFromResource(object|string $resource, int $referenceType = UrlGeneratorInterface::ABS_PATH, ?Operation $operation = null, array $context = []): string;
 }