Shall I set an empty string computed string attribute for Terraform resource?

Question

context: I'm adding a new resource to TF Provider.

I've got an API that optionally return a string attribute so I represent it as:

"foo": {
  Type:        schema.TypeString,
  Computed:    true,
  Optional:    true,
},

Question: if an API returns value not set / empty string for response.foo, shall I still set an empty string for foo attribute or I shouldn't set any value instead (e.g., null)? in my resource schema.

Answer 1

(Hello! I'm the same person who wrote the answer you included in your screenshot.)

If both approaches -- returning null or returning an empty string -- were equally viable from a technical standpoint then I would typically prefer to use null to represent the absence of a value, since that is clearly distinct from an empty string which for some situations would otherwise be a valid present value for the attribute.

However, since it seems like you are using the old SDK ("SDKv2") here, you will probably be constrained from a technical standpoint: SDKv2 was designed for Terraform v0.11 and earlier and so it predates the idea of attributes being null and so there is no way in its API to specify that. You may be able to "trick" the SDK into effectively returning null by not calling d.Set("foo", ...) at all in your Create function, but there is no API provided to unset an attribute and so once you've set it to something non-null there would typically be no way to get it to go back to being null again.

Given that, I'd suggest it better to be consistent and always use "" when using the old SDK, because that way users of the provider won't have to deal with the inconsistency of the value sometimes being null and sometimes being "" in this case.

When using the modern Terraform Plugin Framework this limitation doesn't apply, because that framework was designed with the modern Terraform language in mind. You aren't using that framework and so this part of the answer probably won't help you right now, but I'm mentioning it just in case someone else finds this answer in future who might already be using or be considering use of the new framework.