fix: isnull of empty add quotes

Author: vaggeliskls

Vagrantfile

@@ -43,7 +43,7 @@ Vagrant.configure("2") do |config|
             Write-Host "Running  $runner";
             $random = -join ((48..57) + (97..122) | Get-Random -Count 8 | % {[char]$_});
             Expand-Archive -LiteralPath ${GITHUB_RUNNER_FILE} -DestinationPath runner-$random -Force;
-            if (![string]::IsNullOrEmpty(${PAT})) {
+            if (![string]::IsNullOrEmpty("${PAT}")) {
                 Invoke-Expression -Command "C:\\runner-$random\\config.cmd --name ${GITHUB_RUNNER_NAME}_$random --replace --unattended --url ${RUNNER_URL} --labels ${GITHUB_RUNNER_LABELS} --pat ${PAT}";
             } else {
                 Invoke-Expression -Command "C:\\runner-$random\\config.cmd --name ${GITHUB_RUNNER_NAME}_$random --replace --unattended --url ${RUNNER_URL} --labels ${GITHUB_RUNNER_LABELS} --token ${TOKEN}";