diff --git a/scripts/upgrade b/scripts/upgrade
index 6bf26b1..1d7b700 100755
--- a/scripts/upgrade
+++ b/scripts/upgrade
@@ -41,13 +41,13 @@ then
 fi
 
 # If email doesn't exist, create it
-if [ -z "$email" ]; then
+if [ -z "${email:-}" ]; then
 	email=$(ynh_user_get_info --username=$admin --key=mail)
 	ynh_app_setting_set --app=$app --key=email --value=$email
 fi
 
 # If language doesn't exist, create it
-if [ -z "$language" ]; then
+if [ -z "${language:-}" ]; then
 	language="en"
 	ynh_app_setting_set --app=$app --key=language --value=$language
 fi