Session variable is deleted or set to "assets"

[cpx3]

Hi co-programmers,

I try to write the value of an url segment to a session. All works fine as long as there IS a segment, but the moment there is no segment, my values are set to empty or to "assets".

My code is 

if ($input->urlSegment1 && !empty($input->urlSegment1)) {$session->set("region", $input->urlSegment1);}

I just want the session-value to be left alone when I go back to the start page (which has no segments) and not to be changed. Any ideas what I am doing wrong?

Thanks,

Bernhard