diff --git a/src/SpecBaseObject.php b/src/SpecBaseObject.php
index 29f70b4..6e87c1f 100644
--- a/src/SpecBaseObject.php
+++ b/src/SpecBaseObject.php
@@ -302,13 +302,23 @@ protected function hasProperty(string $name): bool
         return isset($this->_properties[$name]) || isset($this->attributes()[$name]);
     }
 
-    protected function requireProperties(array $names)
+    protected function requireProperties(array $names, array $atLeastOne = [])
     {
         foreach ($names as $name) {
             if (!isset($this->_properties[$name])) {
                 $this->addError(" is missing required property: $name", get_class($this));
             }
         }
+
+        if (count($atLeastOne) > 0) {
+            foreach ($atLeastOne as $name) {
+                if (array_key_exists($name, $this->_properties)) {
+                    return;
+                }
+            }
+
+            $this->addError(" is missing at least one of the following required properties: " . implode(', ', $atLeastOne), get_class($this));
+        }
     }
 
     protected function validateEmail(string $property)
diff --git a/src/spec/OpenApi.php b/src/spec/OpenApi.php
index c45fbad..7476ce8 100644
--- a/src/spec/OpenApi.php
+++ b/src/spec/OpenApi.php
@@ -20,6 +20,7 @@
  * @property Server[] $servers
  * @property Paths|PathItem[] $paths
  * @property Components|null $components
+ * @property PathItem[]|null $webhooks
  * @property SecurityRequirement[] $security
  * @property Tag[] $tags
  * @property ExternalDocumentation|null $externalDocs
@@ -46,6 +47,7 @@ protected function attributes(): array
             'info' => Info::class,
             'servers' => [Server::class],
             'paths' => Paths::class,
+            'webhooks' => [PathItem::class],
             'components' => Components::class,
             'security' => [SecurityRequirement::class],
             'tags' => [Tag::class],
@@ -83,7 +85,12 @@ public function __get($name)
      */
     public function performValidation()
     {
-        $this->requireProperties(['openapi', 'info', 'paths']);
+        if ($this->getMajorVersion() === static::VERSION_3_0) {
+            $this->requireProperties(['openapi', 'info', 'paths']);
+        } else {
+            $this->requireProperties(['openapi', 'info'], ['paths', 'webhooks', 'components']);
+        }
+
         if (!empty($this->openapi) && !preg_match(static::PATTERN_VERSION, $this->openapi)) {
             $this->addError('Unsupported openapi version: ' . $this->openapi);
         }
diff --git a/src/spec/Schema.php b/src/spec/Schema.php
index 59eb425..5e96230 100644
--- a/src/spec/Schema.php
+++ b/src/spec/Schema.php
@@ -40,7 +40,7 @@
  * @property string[] $required list of required properties
  * @property array $enum
  *
- * @property string $type
+ * @property string|string[] $type type can only be `string` in OpenAPI 3.0, but can be an array of strings since OpenAPI 3.1
  * @property Schema[]|Reference[] $allOf
  * @property Schema[]|Reference[] $oneOf
  * @property Schema[]|Reference[] $anyOf
diff --git a/src/spec/Type.php b/src/spec/Type.php
index 9861000..b4c8123 100644
--- a/src/spec/Type.php
+++ b/src/spec/Type.php
@@ -21,6 +21,7 @@ class Type
     const BOOLEAN = 'boolean';
     const OBJECT = 'object';
     const ARRAY = 'array';
+    const NULL = 'null'; // Since OpenAPI 3.1
 
     /**
      * Indicate whether a type is a scalar type, i.e. not an array or object.
@@ -38,6 +39,7 @@ public static function isScalar(string $type): bool
             self::NUMBER,
             self::STRING,
             self::BOOLEAN,
+            self::NULL,
         ]);
     }
 }
diff --git a/tests/spec/OpenApiTest.php b/tests/spec/OpenApiTest.php
index 2cb4024..99b3346 100644
--- a/tests/spec/OpenApiTest.php
+++ b/tests/spec/OpenApiTest.php
@@ -17,7 +17,7 @@ public function testEmpty()
         $this->assertEquals([
             'OpenApi is missing required property: openapi',
             'OpenApi is missing required property: info',
-            'OpenApi is missing required property: paths',
+            'OpenApi is missing at least one of the following required properties: paths, webhooks, components',
         ], $openapi->getErrors());
 
         // check default value of servers
@@ -232,10 +232,15 @@ public function testSpecs($openApiFile)
         $this->assertAllInstanceOf(\cebe\openapi\spec\Server::class, $openapi->servers);
 
         // paths
-        if ($openapi->components !== null) {
+        if ($openapi->paths !== null) {
             $this->assertInstanceOf(\cebe\openapi\spec\Paths::class, $openapi->paths);
         }
 
+        // webhooks
+        if ($openapi->webhooks !== null) {
+            $this->assertAllInstanceOf(\cebe\openapi\spec\PathItem::class, $openapi->webhooks);
+        }
+
         // components
         if ($openapi->components !== null) {
             $this->assertInstanceOf(\cebe\openapi\spec\Components::class, $openapi->components);
diff --git a/tests/spec/PathTest.php b/tests/spec/PathTest.php
index 6c46e4b..d028258 100644
--- a/tests/spec/PathTest.php
+++ b/tests/spec/PathTest.php
@@ -66,7 +66,7 @@ public function testRead()
         }
     }
 
-    public function testCreateionFromObjects()
+    public function testCreationFromObjects()
     {
         $paths = new Paths([
             '/pets' => new PathItem([