Backported return type violation bugfixes.

Author: derrabus

Core/Encoder/EncoderAwareInterface.php

@@ -22,7 +22,7 @@ interface EncoderAwareInterface
      * If the method returns null, the standard way to retrieve the encoder
      * will be used instead.
      *
-     * @return string
+     * @return string|null
      */
     public function getEncoderName();
 }

Core/User/User.php

@@ -69,6 +69,7 @@ public function getPassword()
      */
     public function getSalt()
     {
+        return null;
     }
 
     /**