Fixed a bug in the PowerShell script

PowerShell/post_notices.ps1

@@ -18,12 +18,23 @@ param(
 
     # Defaults to a .env file next to the repo root (one level up from this script),
     # matching where the Python version expects it.
-    [string]$EnvFile = (Join-Path $PSScriptRoot "..\.env")
+    [string]$EnvFile
 )
 
 $ErrorActionPreference = "Stop"
 
-. (Join-Path $PSScriptRoot "PolarisClient.ps1")
+# $PSScriptRoot isn't always populated (e.g. PowerShell 2.0, or the script being
+# dot-sourced/pasted rather than run via -File), so fall back to $MyInvocation.
+$ScriptRoot = $PSScriptRoot
+if (-not $ScriptRoot) {
+    $ScriptRoot = Split-Path -Parent $MyInvocation.MyCommand.Path
+}
+
+if (-not $EnvFile) {
+    $EnvFile = Join-Path $ScriptRoot "..\.env"
+}
+
+. (Join-Path $ScriptRoot "PolarisClient.ps1")
 
 function Import-DotEnv {
     param([string]$Path)