Added Copilot suggestion so Test-IsInGroup consistently returns a boolean. Error paths no longer return $null, which previously caused silent false negatives on transient Graph errors and bypassed caching. Instead, errors are surfaced explicitly and a boolean result is returned in all code paths.

Author: rosspa05

M365/MDO/MDOThreatPolicyChecker.ps1

@@ -194,7 +194,8 @@ begin {
             $groupMembers = Get-MgGroupMember -GroupId $GroupObjectId -All -ErrorAction Stop
         } catch {
             Write-Host "Error getting group members for $GroupObjectId`:`n$_" -ForegroundColor Red
-            return $null
+            $memberCache[$cacheKey] = $false
+            return $false
         }
 
         # Check if the email address is in the group
@@ -209,7 +210,8 @@ begin {
                             $user = Get-MgUser -UserId $member.Id -ErrorAction Stop
                         } catch {
                             Write-Host "Error getting user with Id $($member.Id):`n$_" -ForegroundColor Red
-                            return $null
+                            $memberCache[$cacheKey] = $false
+                            return $false
                         }
                         # Compare the user's email address with the $email parameter
                         if ($user.Mail -eq $Email.ToString()) {