fix(terraform): handle missing thresholds in line widget conversion

[TechIsCool]

Description

The newrelic utils terraform dashboard command fails with a fatal error when processing dashboards that contain line widgets (viz.line) without threshold configuration. This prevents legitimate dashboard JSON exports from New Relic from being converted to Terraform HCL format.

Go Version

go version go1.25.1 darwin/arm64

Current behavior

When attempting to convert a New Relic dashboard JSON to Terraform HCL format, the CLI immediately crashes with a fatal error if any line widget in the dashboard doesn't have thresholds configured:

cat example_mvp.json | newrelic utils terraform dashboard --label test
FATAL Error unmarshalling widgetLineThreshold:unexpected end of JSON input

The command terminates without producing any output.

Expected behavior

The command should successfully convert the dashboard JSON to Terraform HCL format. Line widgets without thresholds are valid in New Relic dashboards (thresholds are optional), so the conversion should handle their absence gracefully and generate valid Terraform configuration.

Steps To Reproduce

1. Create a JSON file named example_mvp.json with the following content:

{
  "name": "MVP Dashboard",
  "description": "Minimal dashboard to reproduce line widget threshold issue",
  "permissions": "PUBLIC_READ_ONLY",
  "pages": [
    {
      "name": "Test Page",
      "description": "Page with line widget without thresholds",
      "widgets": [
        {
          "id": "1",
          "title": "Line Widget Without Thresholds",
          "layout": {
            "column": 1,
            "row": 1,
            "width": 4,
            "height": 3
          },
          "linkedEntityGuids": null,
          "visualization": {
            "id": "viz.line"
          },
          "rawConfiguration": {
            "facet": {},
            "legend": {
              "enabled": true
            },
            "nrqlQueries": [
              {
                "accountId": 12345,
                "query": "SELECT count(*) FROM Transaction TIMESERIES"
              }
            ],
            "platformOptions": {},
            "yAxisLeft": {
              "zero": false
            }
          }
        }
      ]
    }
  ]
}

2. Run the command:

cat example_mvp.json | newrelic utils terraform dashboard --label test

3. See error:

FATAL Error unmarshalling widgetLineThreshold:unexpected end of JSON input

Debug Output (if applicable)

FATAL Error unmarshalling widgetLineThreshold:unexpected end of JSON input

The error originates from internal/utils/terraform/dashboard.go:293 in the writeLineWidgetAttributes() function, which unconditionally attempts to unmarshal the config.Threshold field even when it's empty or null.

Additional Context

• This issue affects any dashboard exported from New Relic containing line widgets without threshold configuration
• Line widgets are one of the most common widget types in New Relic dashboards
• The thresholds field is optional in New Relic's dashboard API specification
• The example_mvp.json file triggers this issue as it contains multiple line widgets without thresholds
• The root cause is in the writeLineWidgetAttributes() function which doesn't validate that threshold data exists before attempting to unmarshal it

References or Related Issues

• Affected file: internal/utils/terraform/dashboard.go
• Affected function: writeLineWidgetAttributes()
• Affected command: newrelic utils terraform dashboard

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[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}