Remove empty Empty List of Variant

Did you give a!flatten a try?

docs.appian.com/.../fnc_array_a_flatten.html

Yes, but I need to preserve the inner list of tasks, and after using `a!flatten`, I obtain a general list of tasks. Is there a way to preserve the lists and eliminate the empty ones? 

By any chance did you try reject( fn!isnull, Result) ??

Appian is bad at supporting list of list, unless you involve a map. You can remove the empty values directly when you are building this output using the reject() function or adding an if() condition to check if the value is nullorempty, if yes, then just add {} as the output for that iteration. Appian cannot print in a list unless all are {}

Try with this (from localtmp to the end , replace the name of your list)

a!localVariables(
local!inputArray: {1,2,3,4,5,6,7,8,9,10,"","","",""},
local!totalArray: length(local!inputArray),
local!maximumPerArray: 5,

local!amountArrays: ceiling(local!totalArray / local!maximumPerArray),
local!iterationArray: enumerate(local!amountArrays),
local!res:
a!forEach(
items: local!iterationArray,
expression: with(
local!leftAmountToCut: fv!item * local!maximumPerArray,
local!rightAmountToCut: local!totalArray - ((fv!item + 1) * local!maximumPerArray),

rdrop(
ldrop(
local!inputArray,
local!leftAmountToCut
),
if(local!rightAmountToCut < 0, 0, local!rightAmountToCut)
)
)
),

local!tmp:
a!forEach(
items: local!res,
/*expression: if(count(reject(fn!isnull,union(fv!item, fv!item)))>0, union(fv!item, fv!item),null)*/
expression: count(reject(fn!isnull,union(fv!item, fv!item)))>0
),

index(local!res, wherecontains(true, local!tmp))

)