Availability:C-language interface function
bool PL_get_nil_ex(term_t 
l)As PL_get_nil(), 
but raises a type or instantiation error if
t is not the empty list. Because PL_get_nil_ex() 
is commonly used after a while loop over PL_get_list_ex(), 
it fails immediately if there is an exception pending (from PL_get_list_ex()).