diff --git a/src/Types/GenericType.php b/src/Types/GenericType.php
index 2f198ca..345500c 100644
--- a/src/Types/GenericType.php
+++ b/src/Types/GenericType.php
@@ -37,9 +37,9 @@ public function __construct( string $json = null ) {
 	
 	/**
 	 * Ritorna le proprietà della classe serializzabili
-	 * @return array
+	 * @return array|mixed
 	 */
-	public function jsonSerialize() {
+	public function jsonSerialize(): mixed {
 		$properties = [];
 		
 		foreach ( get_object_vars( $this ) as $key => $value ) {