Count function

count() intentionally returns the length of an array including nulls.  if you want to get the length of an array excluding nulls, then you would use length().

Thank you, that makes sense so count is also counting the null.

The one tricky thing about the length() function though is that you may also need to consider if the variable itself is null. For instance, both of these return the same:

length({"test"})
count({"test"})

The one below returns 1 for count and 0 for length:

length({null})
count({null})

However, this one below actually fails when using length (and returns 1 for count()):

length(null)
count(null)

So, if it's possible that the value could be null and not in a list, it's often good practice to pair your length function with a null check like this:

a!localVariables(
  local!data: null,
  if(
    isnull(local!data),
    0,
    length(local!data)
  )
)

Agreed, in most of my systems sooner or later we've implemented an expression rule to do a null-safe length(), like "UTIL_arrayLength()" or similar - just to prevent errors when the inevitable "get length of a null" happens.

Agreed, in most of my systems sooner or later we've implemented an expression rule to do a null-safe length(), like "UTIL_arrayLength()" or similar - just to prevent errors when the inevitable "get length of a null" happens.