IsMissing Function

Kevin, I know how to use the function and have been doing so in my database for quite a number of months.  After the last office 365 update came across, the function returns false when it should (and did for said months) return true.  I have changed the functions/subs I have that use it to also test for a zero value or null string - which solves the problem, but I would rather just keep clean code that can rely on proper results from a built-in function.

IsMissing() only works with a variant argument that has no default value.  Try the code below.  If it returns true, IsMissing is working as it should:

Sub TestSub(Optional v As Variant)
    Debug.Print IsMissing(v)
End Sub

I checked my old code dating back to the '97 days, and all the IsMissing functions were used with variants with no defaults.

None of the following will work with IsMissing:

Sub TestSub(Optional i As Integer)
Sub TestSub(Optional i As Integer = 1)
Sub TestSub(Optional s As String)
Sub TestSub(Optional s As String = "test")
Etc.

In other words, nothing has been changed to IsMissing as far as I see.

It was functioning for months with an optional string variable.  As of the last update, not.

This *2021* documentation says IsMissing only works with variants with no defaults:

     https://learn.microsoft.com/en-us/office/vba/language/reference/user-interface-help/ismissing-function

which says:

"IsMissing does not work on simple data types (such as Integer or Double) because, unlike Variants, they don't have a provision for a 'missing' flag bit."

So either you misremember, or you were misled by something you saw that made you believe so.