Confusing error when `GOOGLE_APPLICATION_CREDENTIALS` not set

[functicons]

The error message is quite confusing when GOOGLE_APPLICATION_CREDENTIALS is not set. For example:

$ terraformer import google --resources=networks,subnetworks --connect=true --regions=us-central1 --projects=my-project
2025/08/03 11:20:51 google importing project my-project region us-central1
2025-08-03T11:20:53.399-0700 [ERROR] plugin.terraform-provider-google_v4.85.0_x5: Response contains error diagnostic: @caller=github.com/hashicorp/[email protected]/tfprotov5/internal/diag/diagnostics.go:55 diagnostic_attribute="" diagnostic_severity=ERROR tf_provider_addr=registry.terraform.io/hashicorp/google tf_req_id=b342fe57-26da-bc92-dcba-e62bb7c88121 tf_rpc=Configure @module=sdk.proto
  diagnostic_detail=
  | An unexpected error was encountered trying to build a value. This is always an error in the provider. Please report the following to the provider developer:
  | 
  | Received null value, however the target type cannot handle null values. Use the corresponding `types` package type, a pointer type or a custom type that handles null values.
  | 
  | Path: 
  | Target Type: fwmodels.ProviderModel
  | Suggested `types` Type: basetypes.ObjectValue
  | Suggested Pointer Type: *fwmodels.ProviderModel
   diagnostic_summary="Value Conversion Error" tf_proto_version=5.3 timestamp=2025-08-03T11:20:53.399-0700

The tool should validate the value and generates actionable error message.