Formula error to manipulate arrays to strike all past due dates and show the latest one

[Rajal Shah]

I am getting all historical values of due date and putting a strikethrough of all past due dates except the latest one.

e.g. for myArray = None -> 2025-04-11 00:00:00.0,

                                2025-04-11 00:00:00.0 -> 2025-04-25 00:00:00.0,

                                2025-04-25 00:00:00.0 -> 2025-06-30 00:00:00.0

The output is: 

However, this formula fails for this myArray and I am unable to debug why that is the case. (Someone is setting and unsetting the value of 5/15/2025..)

myArray = None -> 2025-05-15 00:00:00.0,

                   2025-05-15 00:00:00.0 -> None,

                   None -> 2025-05-15 00:00:00.0

The output I get is 

Here is the code..

WITH myArray = unique( history ) :

// WITH myArray = history.changes.filter($.field = "duedate") :

WITH formattedArray = MAP(myArray,

IF(

$.to = LAST(myArray).to,

$.to,

CONCAT("~~ ", $.to, " ~~")

)

) :

//myArray

//formattedArray

JOIN(formattedArray, ", ", "", "")

Can anyone explain what is going on?