Index expression of filenotpresent

Jenkinsfile

@@ -32,7 +32,13 @@ pipeline {
         } 
 
         stage('Create temporaly directory') {
-            when { expression { return !fileExists ('/var/tmp/opengnsys') } }
+            when {
+                expression {
+                boolean fileNotPresent = !fileExists('/var/tmp/opengnsys')
+                return fileNotPresent
+                }
+            }
+
             steps {
             sh 'mkdir /var/tmp/opengnsys'
             }