Upgrade guide: Add guidance for removing empty strings from `provider…

…` blocks (#9048)

* Add guidance for removing empty strings from `provider` blocks

* Update code block to use tf formatting, instead of diff

mmv1/third_party/terraform/website/docs/guides/version_5_upgrade.html.markdown

@@ -118,6 +118,21 @@ The new annotations model is similar to the new labels model and will be applied
 
 There are now two annotation-related fields with the new model, the `annotations` and the output-only `effective_annotations` fields.
 
+### Updates to how empty strings are handled in the `provider` block
+
+In 5.0.0+ any empty strings set in the `provider` block will be used and not ignored. Previously any empty strings used as arguments in the `provider` block were ignored and did not contribute to configuration of the provider. 
+
+Users should remove empty string arguments to avoid errors during plan/apply stages.
+
+```tf
+provider "google" {
+  credentials = "" # this line should be removed
+  project = "my-project"
+  region = "us-central1"
+  zone = "" # this line should be removed
+}
+```
+
 ### Changes to how default `location`, `region` and `zone` values are obtained for resources
 
 Currently, when configuring resources that require a `location`, `region` or `zone` field you have the choice of specifying it in the resource block or allowing default values to be used. Default [region](https://registry.terraform.io/providers/hashicorp/google/latest/docs/guides/provider_reference#region) or [zone](https://registry.terraform.io/providers/hashicorp/google/latest/docs/guides/provider_reference#zone) values can be configured in the provider block or by providing values through environment variables.