TT#29904 allow /api/numbers undef ac-cc-sn-is_primary

Change-Id: I6a7a8d7d0cc66a25fcae7ffae2c20992125a510a

lib/NGCP/Panel/Role/API/Numbers.pm

@@ -118,7 +118,10 @@ sub update_item {
     my ($self, $c, $item, $old_resource, $resource, $form) = @_;
     my $schema = $c->model('DB');
 
+    # we maybe want to remove such checks to compare readonly fields:
     foreach my $field(qw/cc ac sn is_primary/) {
+        $old_resource->{$field} //= '';
+        $resource->{$field} //= '';
         unless($old_resource->{$field} eq $resource->{$field}) {
             $self->error($c, HTTP_UNPROCESSABLE_ENTITY, "Field '$field' is not allowed to be updated via this API endpoint, use /api/subscriber/\$id instead.");
             return;