fix: Skip limits_per_label_set dynamic block when set to null (#28)

Co-authored-by: Bryant Biggs <bryantbiggs@gmail.com>

Author: Sudokamikaze

main.tf

@@ -38,7 +38,7 @@ resource "aws_prometheus_workspace_configuration" "this" {
   workspace_id             = local.workspace_id
 
   dynamic "limits_per_label_set" {
-    for_each = var.limits_per_label_set
+    for_each = var.limits_per_label_set != null ? var.limits_per_label_set : []
 
     content {
       label_set = limits_per_label_set.value.label_set