fix: handle null secondary_ip_range in cluster_alias_ranges_cidr

[raman1236]

Description

Fixes #564

When using add_cluster_firewall_rules=true and performing terraform destroy, or when the subnetwork data source returns null secondary_ip_range, Terraform fails with:

Error: Iteration over null value

A null value cannot be used as the collection in a 'for' expression.

Root Cause

The cluster_alias_ranges_cidr local iterates over data.google_compute_subnetwork.gke_subnetwork[0].secondary_ip_range directly. During destroy operations (or certain edge cases), this value can be null instead of an empty list, causing the error.

Solution

This fix uses coalesce() to default null secondary_ip_range to an empty list:

# Before
cluster_alias_ranges_cidr = var.add_cluster_firewall_rules ? { for range in toset(data.google_compute_subnetwork.gke_subnetwork[0].secondary_ip_range) : range.range_name => range.ip_cidr_range } : {}

# After  
cluster_alias_ranges_cidr = var.add_cluster_firewall_rules ? { for range in toset(coalesce(data.google_compute_subnetwork.gke_subnetwork[0].secondary_ip_range, [])) : range.range_name => range.ip_cidr_range } : {}

Affected Modules

Applied the fix consistently across all modules that use this pattern:

• Root module
• beta-private-cluster-update-variant
• private-cluster
• beta-public-cluster
• beta-private-cluster
• beta-autopilot-public-cluster
• beta-autopilot-private-cluster
• private-cluster-update-variant
• beta-public-cluster-update-variant

Testing

• The fix is backward compatible - when secondary_ip_range is not null, behavior is identical
• When null, returns empty map instead of error
• No configuration changes required for users

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[gemini-code-assist]

Code Review

This pull request enhances several GKE modules by adding the coalesce function to handle potential null values in secondary_ip_range and refactoring logging_config logic to use a new logging_config_is_set local variable. These changes ensure more reliable resource creation and clearer conditional logic for logging components. I have no feedback to provide.