gitlab_instance_service_account api error when not specifying username

It seems when no username (this is optional so valid) is configured in the gitlab_instance_service_account resource an empty string is sent to the gitlab api. This isn't a valid username and the api returns a 400.

Example resource:

resource "gitlab_instance_service_account" "example_sa" {
  name     = "example-name"
  group    = 123456
}

Apply failure output:

│ Unable to create service account: POST
│ https://gitlab.com/api/v4/groups/XXXXXXXX/service_accounts: 400 {message:
│ 400 Bad request - Username can't be blank, Username can't be blank,
│ Username can only include non-accented letters, digits, '_', '-' and '.'.
│ It must not start with '-', '_', or '.', nor end with '-', '_', '.',
│ '.git', or '.atom'., Username can contain only letters, digits, '_', '-'
│ and '.'. Cannot start with '-' or end in '.', '.git' or '.atom'., Username
│ is too short (minimum is 2 characters), and Username is too short (minimum
│ is 1 character)}

I think the bug is located here:

https://gitlab.com/gitlab-org/terraform-provider-gitlab/-/blob/97bff1a023b8372ee6ddb93a4b4e7ff6aee5e57f/internal/provider/resource_gitlab_group_service_account.go#L123

It seems username being not being specified will use the default string value in Go.

This is probably the same for the name attribute which is also optional.

• provider version: 18.1.1
• tf version: 1.6.2