not an array error in PHP5

PHP5 (the only one I use) gives the following error when trying to show a map:
warning: array_merge() [function.array-merge]: Argument #1 is not an array in /home/example/modules/gmap/gmap.module on line 619.

The line in question is:
$tt=array_merge($tt,gmap_dopoint($ttt[$i],$ver));

at this point $tt is not initialized, so the following code will work:
$tt=gmap_dopoint($ttt[$i],$ver);

Marius