how to remove all nulls in array and get the corresponding index of the null value

Hi,

Please try this. I made a small change in your code.

a!localVariables(
local!arr: { 1, 2, null, 3, null },
local!val: { 1, 2, 3, 4, 5 },
/*Get null indices */
local!getNullIndices: a!forEach(
items: local!arr,
expression: if(isnull(fv!item), fv!index, null())
),
local!removeNullIndices: remove(
local!getNullIndices,
where(
a!forEach(
items: local!getNullIndices,
expression: if(a!isNullOrEmpty(fv!item), true, false)
)
)
),

/* Required Output */
local!data: remove(
local!val,
local!removeNullIndices
),
local!data
)

This is done much more simply by building a new array and leaving out the blank members (forget the remove() function altogether please).

a!flatten(
  a!forEach(
    ri!array,
    if(
      a!isNotNullOrEmpty(fv!item),
      fv!item,
      {}
    )
  )
)

Note: The above works without a!flatten() up until you have an instance where all items in the array are blank.  A quirk of the data a!forEach() returns is an array of empty sets is returned when they're all empty (but when any entry is nonempty, the empty sets are ignored from the results).  Wrapping the whole thing in a!flatten() corrects this.