From efb3c8056a0ba69f831303dac2d82e53511704f5 Mon Sep 17 00:00:00 2001
From: Notselwyn <68616630+Notselwyn@users.noreply.github.com>
Date: Fri, 14 Apr 2023 21:18:08 +0200
Subject: [PATCH] fix: fixed crash when env var "computername" does not exist

---
 SafeExamBrowser.SystemComponents/VirtualMachineDetector.cs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/SafeExamBrowser.SystemComponents/VirtualMachineDetector.cs b/SafeExamBrowser.SystemComponents/VirtualMachineDetector.cs
index a157e95b..5294d825 100644
--- a/SafeExamBrowser.SystemComponents/VirtualMachineDetector.cs
+++ b/SafeExamBrowser.SystemComponents/VirtualMachineDetector.cs
@@ -136,7 +136,9 @@ namespace SafeExamBrowser.SystemComponents
 
 			// check Windows timeline caches for current hardware config
 			var deviceCacheKey = Microsoft.Win32.Registry.CurrentUser.OpenSubKey($"SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\TaskFlow\\DeviceCache");
-			if (deviceCacheKey != null)
+			var currHostname = System.Environment.GetEnvironmentVariable("COMPUTERNAME");
+
+			if (deviceCacheKey != null && currHostname != null)
 			{
 				foreach (var cacheId in deviceCacheKey.GetSubKeyNames())
 				{
@@ -147,7 +149,6 @@ namespace SafeExamBrowser.SystemComponents
 						continue;
 					}
 
-					var currHostname = System.Environment.GetEnvironmentVariable("COMPUTERNAME").ToLower();
 					var cacheHostname = ((string) cacheKey.GetValue("DeviceName")).ToLower();
 
 					// windows timeline syncs with other hosts that a user has logged into: check hostname to only check this device