Wrap last login in optionalNullable

Author: Sheikah45

src/main/java/com/faforever/api/user/MeController.java

@@ -60,7 +60,7 @@ public JsonApiDocument me(@AuthenticationPrincipal FafUserDetails authentication
             .tag(player.getClan().getTag())
             .name(player.getClan().getName())
             .build(),
-          "lastLogin", player.getLastLogin(),
+          "lastLogin", Optional.ofNullable(player.getLastLogin()),
           "groups", groups,
           "permissions", grantedAuthorities
         ),