diff --git a/src/Database.php b/src/Database.php
index 868945a..c76e550 100644
--- a/src/Database.php
+++ b/src/Database.php
@@ -268,10 +268,10 @@ public function getRepository(string $klass): Repository
      * @psalm-return ?TEntity
      *
      * @param string $klass Entity class name
-     * @param int $id ID of the entity
+     * @param ?int $id ID of the entity
      * @return ?Entity
      */
-    public function findOne(string $klass, int $id): ?Entity
+    public function findOne(string $klass, ?int $id): ?Entity
     {
         return $this->getRepository($klass)->findOne($id);
     }
diff --git a/src/Repository.php b/src/Repository.php
index 603d7c2..8dd5b23 100644
--- a/src/Repository.php
+++ b/src/Repository.php
@@ -79,11 +79,15 @@ public function __construct(Database $db, string $klass)
     /**
      * Find a single entity by its ID
      *
-     * @param int $id ID of the entity
+     * @param ?int $id ID of the entity
      * @psalm-return ?TEntity
      */
-    public function findOne(int $id): ?Entity
+    public function findOne(?int $id): ?Entity
     {
+        if ($id === null) {
+            return null;
+        }
+        
         return $this->findOneBy([
             'id' => $id,
         ]);