diff --git a/backend_modules/null/base/variables.tf b/backend_modules/null/base/variables.tf
index 7a77bab77..96d75fb4a 100644
--- a/backend_modules/null/base/variables.tf
+++ b/backend_modules/null/base/variables.tf
@@ -86,5 +86,5 @@ variable "is_server_paygo_instance" {
 variable "product_version" {
   description = "One of: 4.3-nightly, 4.3-released, 4.3-pr, 4.3-beta, 4.3-VM-nightly, 4.3-VM-released, 5.0-nightly, 5.0-released, head, uyuni-master, uyuni-released, uyuni-pr"
   type        = string
-  default     = ""
+  default     = null
 }