diff --git a/src/DSN/DSN.php b/src/DSN/DSN.php
index 0eb0ef2..c6d5746 100644
--- a/src/DSN/DSN.php
+++ b/src/DSN/DSN.php
@@ -5,9 +5,9 @@
 class DSN
 {
     /**
-     * @var string
+     * @var ?string
      */
-    protected string $scheme;
+    protected ?string $scheme;
 
     /**
      * @var ?string
@@ -71,9 +71,9 @@ public function __construct(string $dsn)
     /**
      * Return the scheme.
      *
-     * @return string
+     * @return ?string
      */
-    public function getScheme(): string
+    public function getScheme(): ?string
     {
         return $this->scheme;
     }