[sentry]

Fixes TypeError Cannot read properties of null (reading 'quantity') on /checkout/.

Problem

When customers migrated to the billing platform submit scheduled changes (e.g. downgrades or term renewals deferred to period end), /customers/{slug}/subscription/?expand=invoice returns 204 with no immediate invoice. The checkout success page displays scheduled changes using previewData.invoiceItems.

serialize_billing_platform_subscription_preview serializes invoice items with "data": null. ScheduledChanges in checkoutSuccess.tsx evaluates item.data.quantity ?? 0 for reserved volume line items, which throws a TypeError when data is null.

Fix

• Optional chain item.data?.quantity ?? 0 at both reservedVolume.map call sites in checkoutSuccess.tsx.
• Update BaseInvoiceItem.data type to allow null to reflect actual backend serialization.
• Add optional chaining to purchasedPlanItem.data?.plan in views/amCheckout/index.tsx.
• Add a unit test covering rendering scheduled changes when a reserved line item has data: null.

Legal Boilerplate

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Fixes JAVASCRIPT-3G4X

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