Array with no items but length still > 0

RE: Array with no items but length still > 0

stevenh6272 — Fri, 31 Oct 2025 12:33:51 GMT

Yep. Tested and it works. Thank you.

RE: Array with no items but length still > 0

Harsha Sharma — Fri, 31 Oct 2025 12:25:58 GMT

Given the usecase length() function is not suitable here. It seems length() in expression 2 is considered as a string rather than an array which is why 1 is returned. Below code might explain the deviation between 0 sometimes and sometimes 1. The difference is just whether its an array or not.

a!map(
  arrayLength: length({ "" }), /*returns 0*/
  stringLength: length("") /*returns 1*/
)

So, In practice, as mentioned by almost everyone here, a!isNullOrEmpty() is best solution for cases like this.

RE: Array with no items but length still > 0

stevenh6272 — Fri, 31 Oct 2025 12:25:46 GMT

So, overall, the answer is to use isNullOrEmpty to test a list for no items. I had never considered this thinking it was more a string function than an array functions.

Still, there is a technical nuance here I would like to understand if I can (and if I even have time to). It may have something to do with what osanchea is saying about using Map vs Dictionary. I might try to play with that and see if it helps.

Thank you, all for your responses!!

RE: Array with no items but length still > 0

stevenh6272 — Fri, 31 Oct 2025 12:23:21 GMT

What I learn from your blog is essentially that I should be using isNullOrEmpty (the same thing everyone else here is saying). I don't have a need for the edge cases you mention, but it is good info to know about.

RE: Array with no items but length still > 0

stevenh6272 — Fri, 31 Oct 2025 12:22:10 GMT

You are correct in that isNullOrEmpty does return true in this case.

RE: Array with no items but length still > 0

stevenh6272 — Fri, 31 Oct 2025 12:21:40 GMT

You are correct in that isNullOrEmpty does return true in this case.

RE: Array with no items but length still > 0

stevenh6272 — Fri, 31 Oct 2025 12:21:06 GMT

You are correct in that isNullOrEmpty does return true in this case.

RE: Array with no items but length still > 0

stevenh6272 — Fri, 31 Oct 2025 12:17:15 GMT

And yet, within SH_ErrorGenertor length() did return 0. Why does it sometimes return 0 and sometime return 1 for the same value?

RE: Array with no items but length still > 0

stevenh6272 — Fri, 31 Oct 2025 12:09:21 GMT

I'm not looking for a string to be empty.... I'm looking to see if an array is empty. Why would length(someArray) be 1 if there are no items in the array? That doesn't make any sense.

RE: Array with no items but length still > 0

Stefan Helzle — Fri, 31 Oct 2025 07:47:16 GMT

In this blog post, I try to cover how to check for empty data.

https://appian.rocks/2022/10/17/the-magic-of-null-checking/

RE: Array with no items but length still > 0

Harsha Sharma — Fri, 31 Oct 2025 05:54:00 GMT

The expression for local!anyErrors in expression 2 checks if error is not null as well as its length. Though the local!errors is having 0 items yet as the function length("") returns 1. So length will return true. Similarly behavior of isnull() can be understood from below.

not(isnull({""})) returns true
not(isnull("")) returns false

 length("")   /*returns true*/
not(isnull({""})) /*returns true with a List of empty string*/
not(isnull("")) /*returns false with empty string*/

Given the behavior and working of isnull() and length() the value for local!anyErrors in expression 2 seems fine. To properly check and correct the behavior as per your requirement I suggest you to either replace the local!anyErrors definition with a!isNotNullOrEmpty(local!errors) or simply use local!result.anyErrors.

local!anyErrors: a!isNotNullOrEmpty(local!errors) or,
local!anyErrors: local!result.anyErrors /* Either of these*/

RE: Array with no items but length still > 0

osanchea — Fri, 31 Oct 2025 05:27:28 GMT

When you use index() or dot notation, the value returned is a variant. This can produce a different result when you use the length() function.

To resolve this issue, create a map instead of a dictionary, because values stored in maps are not wrapped in a variant.

Additionally, according to the Appian documentation:
When you pass an empty array to the isnull() function, it returns false. To check whether an empty list is null, use the a!isNullOrEmpty() function instead.

RE: Array with no items but length still > 0

Shubham Aware — Fri, 31 Oct 2025 04:36:23 GMT

Appian treats lists with empty strings as having length, but they cannot be indexed.
Use a!isNullOrEmpty() to check for real errors instead of length().

RE: Array with no items but length still > 0

stevenh6272 — Fri, 31 Oct 2025 00:51:31 GMT

Actually, your scenario does not faithfully represent my code above. You are, indeed, using an array of variant by specifying {} without any qualification. I explicitly cast my data to List<string> (see first code segment above).

I don't think this will repro without using 2 expression rules. As I showed in my example, within the first expression rule, it does, rightly, know the array is empty. It's not until it is returned to the calling expression rule that the weirdness ensues.

RE: Array with no items but length still > 0

osanchea — Thu, 30 Oct 2025 22:43:46 GMT

I’ve tried to replicate your case, and it seems that when you’re indexing the value “local!result.error”, it’s returning a list of variants. That’s why you’re getting the error you mentioned.

RE: Array with no items but length still > 0

stevenh6272 — Thu, 30 Oct 2025 20:21:58 GMT

A small tweak shows the second expression sees the array as having 1 element.

a!localVariables(
  local!result: rule!SH_ErrorGenerator(),
  local!errors: local!result.errors,
  local!anyErrors: and(not(isnull(local!errors)), length(local!errors) > 0),
  {
    a: local!anyErrors,
    b: length(local!errors)
  }
)

But, of course, you cannot actually index that item.

a!localVariables(
  local!result: rule!SH_ErrorGenerator(),
  local!errors: local!result.errors,
  local!anyErrors: and(not(isnull(local!errors)), length(local!errors) > 0),
  {
    a: local!anyErrors,
    b: length(local!errors),
    c: local!errors[1]
  }
)