diff --git a/ecr-repositories.tf b/ecr-repositories.tf
index 6fb4b69..4d1f881 100644
--- a/ecr-repositories.tf
+++ b/ecr-repositories.tf
@@ -7,6 +7,6 @@ resource "aws_ecr_repository" "default" {
 
   encryption_configuration {
     encryption_type = "KMS"
-    kms_key         = length(var.kms_key_arn) > 0 ? var.kms_key_arn : null
+    kms_key         = length(var.kms_key_arn) > 0 ? var.kms_key_arn : ""
   }
 }