diff --git a/scripts/upgrade b/scripts/upgrade
index 995b7a7..0198bfb 100644
--- a/scripts/upgrade
+++ b/scripts/upgrade
@@ -60,7 +60,7 @@ else
 fi
 
 # Retrieve the password from the .env file
-if [ -z "$password" ]; then
+if [ -z "${password:-}" ]; then
 	password=$(ynh_read_var_in_file --file="$install_dir/.env" --key="MINIO_ROOT_PASSWORD")
 fi