Error when issuing ssdp subscribe

In my device handler I see this error :
error java.lang.NullPointerException: Cannot invoke method checkLocationAttribute() on null object @line 68 (ssdpSubscribe)
debug ***** ‘ssdp subscribe’

code used for this error:

  1. what does this error mean?

  2. is my use of the preference input $searchTest right?

  3. any more hints?

  4. seems that if I change from location to null it works:

    subscribe(null, “ssdpTerm.urn:schemas-upnp-org:device:ZonePlayer:1”, ssdpHandler)

Thanks to the helpers