fix: guard against null error body in ErrorResponseHandlerV2

[AshwinBhatkal]

Pull Request

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📄 Summary

ErrorResponseHandlerV2 crashed when response.data.error was null or undefined (e.g. on a timeout or auth error with a non-standard server response body), causing a secondary TypeError on top of the original API error.

Issues closed by this PR

Closes https://github.com/SigNoz/engineering-pod/issues/4284
Closes https://github.com/SigNoz/engineering-pod/issues/4286

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✅ Change Type

• 🐛 Bug fix

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🐛 Bug Context

Root Cause

response.data.error.code / .message / .url / .errors were accessed without any null guard. When the server returns a response without the expected error envelope (e.g. a proxy timeout or a plain auth rejection), response.data.error is null/undefined, causing a crash before the APIError can be thrown.

Fix Strategy

Extract response.data?.error into a variable and use optional chaining with fallbacks for each field, so a well-formed APIError is always thrown regardless of response body shape.

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🧪 Testing Strategy

• Tests added/updated: N/A
• Manual verification: Dashboard save with a timeout or auth error surfaces a proper error message instead of crashing
• Edge cases covered: null response body, missing error field, partial error objects

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⚠️ Risk & Impact Assessment

• Blast radius: Only affects ErrorResponseHandlerV2 — all API calls using this handler
• Potential regressions: None — fallback values match what was previously assumed to always be present
• Rollback plan: Revert the 5-line change

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📝 Changelog

Field	Value
Deployment Type	Cloud / OSS / Enterprise
Change Type	Bug Fix
Description	Fixed crash in API error handler when server response body is missing the error envelope

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📋 Checklist

• Tests added or explicitly not required
• Manually tested
• Breaking changes documented
• Backward compatibility considered

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