bug: workflow_template_revision create sends driftCron: "" when drift_cron is unset, API returns 400

Provider version

1.12.1 (code on main / 1.12.2-rc4 is identical)

Terraform / OpenTofu version

Terraform v1.14.9 on darwin_arm64

Which API region?

EU

Affected resources or data sources

stackguardian_workflow_template_revision (likely also stackguardian_workflow_git and stackguardian_stack_template_revision, which use the same terraform_config conversion)

Terraform configuration

resource "stackguardian_workflow_template" "example" {
  template_name      = "my-template"
  source_config_kind = "TERRAFORM"
  is_public          = "0"
}

resource "stackguardian_workflow_template_revision" "v1" {
  template_id        = stackguardian_workflow_template.example.id
  source_config_kind = "TERRAFORM"
  is_public          = "0"
  user_job_cpu       = 512
  user_job_memory    = 1024

  terraform_config = {
    terraform_version = "1.5.7"
  }
}

What did you expect to happen?

The revision is created with terraformVersion set and no drift schedule, since drift_cron is optional and was not configured.

What actually happened?

terraform apply fails on create:

Error: failed to create template revision

  on main.tf line 35, in resource "stackguardian_workflow_template_revision" "v1":
  35: resource "stackguardian_workflow_template_revision" "v1" {

400: {"msg":"TerraformConfig.driftCron: This field may not be blank.","data":{"fieldErrors":{"TerraformConfig.driftCron":["This field may not be blank."]}}}

Root cause: in internal/resource/workflow_template_revision/model.go, ConvertTerraformConfigToAPI decodes the object with

terraformConfigObj.As(ctx, &terraformConfigModel, basetypes.ObjectAsOptions{
    UnhandledNullAsEmpty:    true,
    UnhandledUnknownAsEmpty: true,
})

At create time the Optional+Computed sub-attributes of terraform_config (drift_cron, terraform_plan_options, terraform_init_options, terraform_bin_path, ...) are unknown in the plan, so they are decoded as "". DriftCron: terraformConfigModel.DriftCron.ValueStringPointer() then yields a non-nil pointer to an empty string, and omitempty on *string in sg-sdk-go (TerraformConfig.DriftCron, v1.5.6) does not drop a non-nil pointer. The request therefore carries "driftCron": "", which the API rejects.

Suggested fix: drop UnhandledNullAsEmpty / UnhandledUnknownAsEmpty (or check IsNull() || IsUnknown() per field) so unset string fields stay nil and are omitted from the payload. The same pattern in the other Convert*ToAPI helpers is worth auditing.

Related: #136 (perpetual diff / computed fields becoming unknown on this resource), #135 (import does not set template_id).

Before submitting

• I have removed all credentials and org-identifying values from the above.

Start in internal/resource/workflow_template_revision/model.go at ConvertTerraformConfigToAPI, then compare the terraform_config conversion used by stackguardian_workflow_git and stackguardian_stack_template_revision. Verify that unset Optional+Computed fields remain absent from the create payload, especially driftCron, and that the API accepts the resulting request.