fix(blockStorage): Prevent panic while detaching block storage

[wonchulee]

• It adds a guard to prevent panic in the detaching block storage step in a specific case.

• reproduce condition

  • User creates KVM server and attaches block storage by themself (using Terraform)
  • destroy the server but keep the block storage

Step 1.

resource "ncloud_server" "kvm-server" {
  subnet_no                 = ncloud_subnet.subnet_private.id
  name                      = "tf-kvm-server"
  server_image_number       = data.ncloud_server_image_numbers.kvm-image.image_number_list.0.server_image_number
  server_spec_code          = data.ncloud_server_specs.kvm-spec.server_spec_list.0.server_spec_code
  login_key_name            = ncloud_login_key.kvm-loginkey.key_name
}

resource "ncloud_block_storage" "kvm-storage" {
  size = "10"
  server_instance_no = ncloud_server.kvm-server.id
  name = "tf-kvm-storage"
  hypervisor_type = "KVM"
  volume_type = "CB1"
  zone = "KR-1"
}

Step 2.

# resource "ncloud_server" "kvm-server" {
#   subnet_no                 = ncloud_subnet.subnet_private.id
#   name                      = "tf-kvm-server"
#   server_image_number       = data.ncloud_server_image_numbers.kvm-image.image_number_list.0.server_image_number
#   server_spec_code          = data.ncloud_server_specs.kvm-spec.server_spec_list.0.server_spec_code
#   login_key_name            = ncloud_login_key.kvm-loginkey.key_name
# }

resource "ncloud_block_storage" "kvm-storage" {
  size = "10"
  
  # server_instance_no = ncloud_server.kvm-server.id
  name = "tf-kvm-storage"
  hypervisor_type = "KVM"
  volume_type = "CB1"
  zone = "KR-1"
}

• Error

│ Error: Request cancelled
│
│ The plugin6.(*GRPCProvider).ApplyResourceChange request was cancelled.
╵

Stack trace from the terraform-provider-ncloud plugin:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0xc0 pc=0x1037402ec]

goroutine 120 [running]:
github.com/terraform-providers/terraform-provider-ncloud/internal/service/server.detachThenWaitServerInstance.func1()
	/Users/wonchul/work/ncloud/terraform/terraform-provider-ncloud/internal/service/server/server.go:1033 +0x2c
github.com/hashicorp/terraform-plugin-sdk/v2/helper/retry.(*StateChangeConf).WaitForStateContext.func1()
	/Users/wonchul/go/pkg/mod/github.com/hashicorp/terraform-plugin-sdk/[email protected]/helper/retry/state.go:113 +0x140
created by github.com/hashicorp/terraform-plugin-sdk/v2/helper/retry.(*StateChangeConf).WaitForStateContext in goroutine 94
	/Users/wonchul/go/pkg/mod/github.com/hashicorp/terraform-plugin-sdk/[email protected]/helper/retry/state.go:86 +0x1d0

Error: The terraform-provider-ncloud plugin crashed!

This is always indicative of a bug within the plugin. It would be immensely
helpful if you could report the crash with the plugin's maintainers so that it
can be fixed. The output above should help diagnose the issue.