It didn’t work because you have a list with sub-lists, which means that you have to add another loop to iterate the sub-lists as well. So this would be something like:
def item_tolist (input):
tolist = input if isinstance(input,list) else [input]
return tolist
var = item_tolist(IN[0])
string = IN[1]
result = []
first_lp_list = []
for lst in var:
if lst == []:
first_lp_list.append(string)
result.append(first_lp_list)
else:
sec_lp_list = []
for item in lst:
if item==[]:
sec_lp_list.append(string)
else:
sec_lp_list.append(item)
result.append(sec_lp_list)
OUT = result
You can also check @AmolShah solution for a similar case.