Narrow existing return types on private/internal/final/test methods

Author: nicolas-grekas

Tests/Authentication/Token/AbstractTokenTest.php

@@ -266,7 +266,7 @@ public function getUserIdentifier(): string
         return $this->name;
     }
 
-    public function getPassword()
+    public function getPassword(): ?string
     {
         return '***';
     }
@@ -284,7 +284,7 @@ public function eraseCredentials()
     {
     }
 
-    public function getSalt()
+    public function getSalt(): ?string
     {
         return null;
     }