diff --git a/functionMap.php b/functionMap.php
index 1692e4f..d352543 100644
--- a/functionMap.php
+++ b/functionMap.php
@@ -70,13 +70,13 @@
     'rest_ensure_response' => ['($response is WP_Error ? WP_Error : WP_REST_Response)'],
     'WP_REST_Request' => [null, '@phpstan-template' => 'T of array', '@phpstan-implements' => 'ArrayAccess<key-of<T>, value-of<T>>'],
     'WP_REST_Request::offsetExists' => [null, 'offset' => 'key-of<T>'],
-    'WP_REST_Request::offsetGet' => ['T[TOffset]', '@phpstan-template' => 'TOffset of key-of<T>', 'offset' => 'TOffset'],
+    'WP_REST_Request::offsetGet' => ['($offset is TOffset ? T[TOffset] : null)', '@phpstan-template' => 'TOffset of key-of<T>', 'offset' => 'TOffset'],
     'WP_REST_Request::offsetSet' => ['void', '@phpstan-template' => 'TOffset of key-of<T>', 'offset' => 'TOffset', 'value' => 'T[TOffset]'],
     'WP_REST_Request::offsetUnset' => ['void', '@phpstan-template' => 'TOffset of key-of<T>', 'offset' => 'TOffset'],
-    'WP_REST_Request::get_param' => ['T[TOffset]', '@phpstan-template' => 'TOffset of key-of<T>', 'key' => 'TOffset'],
+    'WP_REST_Request::get_param' => ['($key is TOffset ? T[TOffset] : null)', '@phpstan-template' => 'TOffset of key-of<T>', 'key' => 'TOffset'],
     'WP_REST_Request::get_params' => ['T'],
     'WP_REST_Request::set_param' => ['void', '@phpstan-template' => 'TOffset of key-of<T>', 'key' => 'TOffset', 'value' => 'T[TOffset]'],
-    'WP_REST_Request::has_param' => [null, 'offset' => 'key-of<T>'],
+    'WP_REST_Request::has_param' => [null, 'key' => 'key-of<T>'],
     'WP_Theme' => [null, '@phpstan-type' => "ThemeKey 'Name'|'Version'|'Status'|'Title'|'Author'|'Author Name'|'Author URI'|'Description'|'Template'|'Stylesheet'|'Template Files'|'Stylesheet Files'|'Template Dir'|'Stylesheet Dir'|'Screenshot'|'Tags'|'Theme Root'|'Theme Root URI'|'Parent Theme'"],
     'WP_Theme::get' => ["(\$header is 'Name'|'ThemeURI'|'Description'|'Author'|'AuthorURI'|'Version'|'Template'|'Status'|'Tags'|'TextDomain'|'DomainPath'|'RequiresWP'|'RequiresPHP'|'UpdateURI' ? (\$header is 'Tags' ? string[] : string) : false)"],
     'WP_Theme::offsetExists' => ['($offset is ThemeKey ? true : false)'],
diff --git a/tests/data/wp_rest_request.php b/tests/data/wp_rest_request.php
index 734b601..119925b 100644
--- a/tests/data/wp_rest_request.php
+++ b/tests/data/wp_rest_request.php
@@ -6,6 +6,19 @@
 
 use function PHPStan\Testing\assertType;
 
+/**
+ * @var \WP_REST_Request<array> $request
+ */
+$request = new WP_REST_Request();
+
+assertType('mixed', $request->get_param('maybeParam'));
+
+assertType('mixed', $request['maybeParam']);
+
+assertType('array', $request->get_params());
+
+assertType('bool', $request->has_param('maybeParam'));
+
 /**
  * @var \WP_REST_Request<array{
  *      stringParam: string,
@@ -18,16 +31,16 @@
 assertType('string', $request->get_param('stringParam'));
 assertType('int', $request->get_param('intParam'));
 assertType('bool', $request->get_param('boolParam'));
-assertType('null', $request->get_param('unknownParam'));
+assertType('null', $request->get_param('nonExistentParam'));
 
 assertType('string', $request['stringParam']);
 assertType('int', $request['intParam']);
 assertType('bool', $request['boolParam']);
-assertType('null', $request['unknownParam']);
+assertType('null', $request['nonExistentParam']);
 
 assertType('array{stringParam: string, intParam: int, boolParam: bool}', $request->get_params());
 
 assertType('bool', $request->has_param('stringParam'));
 assertType('bool', $request->has_param('intParam'));
 assertType('bool', $request->has_param('boolParam'));
-assertType('bool', $request->has_param('unknownParam'));
+assertType('bool', $request->has_param('nonExistentParam'));
diff --git a/wordpress-stubs.php b/wordpress-stubs.php
index adfba41..da47897 100644
--- a/wordpress-stubs.php
+++ b/wordpress-stubs.php
@@ -68946,7 +68946,7 @@ protected function get_parameter_order()
          * @return mixed|null Value if set, null otherwise.
          * @phpstan-template TOffset of key-of<T>
          * @phpstan-param TOffset $key
-         * @phpstan-return T[TOffset]
+         * @phpstan-return ($key is TOffset ? T[TOffset] : null)
          */
         public function get_param($key)
         {
@@ -68961,7 +68961,7 @@ public function get_param($key)
          *
          * @param string $key Parameter name.
          * @return bool True if a param exists for the given key.
-         * @phpstan-param key-of<T> $offset
+         * @phpstan-param key-of<T> $key
          */
         public function has_param($key)
         {
@@ -69261,7 +69261,7 @@ public function offsetExists($offset)
          * @return mixed|null Value if set, null otherwise.
          * @phpstan-template TOffset of key-of<T>
          * @phpstan-param TOffset $offset
-         * @phpstan-return T[TOffset]
+         * @phpstan-return ($offset is TOffset ? T[TOffset] : null)
          */
         #[\ReturnTypeWillChange]
         public function offsetGet($offset)