mailchimp_sync_should_sync_user

Hi.. i use your wonderful plugin but i have a problem.. the filter mailchimp_sync_should_sync_user is not working..

i tryed :

if( $user->has_prop('customfield-newsletter')) {
        return true;
    }

or

if( $user->{'customfield-newsletter'}) {
        return true;
    }

but the result is return is always false.

https://wordpress.org/plugins/mailchimp-sync/