Tep_not_null is_object update

Changed tep_not_null so to chcek if value is object because it returned warnings such as:

Warning: strtolower() expects parameter 1 to be string, object given in
and
Warning: trim() expects parameter 1 to be string, object given in
Merge pull request #162 from gadlol/patch-4

Tep_not_null is_object update