Mastering Windows PowerShell Scripting - Third Edition

The AllowEmptyString attribute

AllowEmptyString fills the gap, allowing both null and empty values to be supplied for a mandatory string parameter. In both cases, the resulting assignment will be an empty string. It is not possible to distinguish between a value passed as null and a value passed as an empty string:

function Test-AllowEmptyString {    [CmdletBinding()]    param (        [Parameter(Mandatory)]        [AllowEmptyString()]        [String]$Parameter1    )}