Allow null as type in schema

src/Chain/StructuredOutput/SchemaFactory.php

@@ -59,6 +59,11 @@ public function buildSchema(string $className): array
             $type = $types[0];
             $propertySchema = $this->getTypeSchema($type);
 
+            // Handle nullable types
+            if (!is_array($propertySchema['type']) && $type->isNullable()) {
+                $propertySchema['type'] = [$propertySchema['type'], 'null'];
+            }
+
             // Add description if available
             if ($description) {
                 $propertySchema['description'] = $description;

tests/Chain/StructuredOutput/ResponseFormatFactoryTest.php

@@ -37,6 +37,7 @@ public function create(): void
                             'format' => 'date-time',
                         ],
                         'isActive' => ['type' => 'boolean'],
+                        'age' => ['type' => ['integer', 'null']],
                     ],
                     'required' => ['id', 'name', 'createdAt', 'isActive'],
                     'additionalProperties' => false,

tests/Chain/StructuredOutput/SchemaFactoryTest.php

@@ -39,6 +39,7 @@ public function buildSchemaForUserClass(): void
                     'format' => 'date-time',
                 ],
                 'isActive' => ['type' => 'boolean'],
+                'age' => ['type' => ['integer', 'null']],
             ],
             'required' => ['id', 'name', 'createdAt', 'isActive'],
             'additionalProperties' => false,

tests/Fixture/StructuredOutput/User.php

@@ -13,4 +13,5 @@ final class User
     public string $name;
     public \DateTimeInterface $createdAt;
     public bool $isActive;
+    public ?int $age = null;
 }