<!--
title: explicit null handling
domain: data-systems
topic: Null Handling
language: TypeScript
source: prisma/prisma
updated: 2025-07-17
url: https://awesomereviewers.com/reviewers/prisma-explicit-null-handling/
-->

Prefer explicit null and undefined handling over optional or nullable types. When possible, provide default values or objects instead of making parameters optional. When null/undefined checks are necessary, handle both values explicitly and use descriptive patterns.

Instead of relying on optional parameters that create chains of conditional access:
```typescript
// Avoid
interface MigrateSetupInput {
  schemaFilter?: MigrateTypes.SchemaFilter
}
// Later: schemaFilter?.['prop'] access

// Prefer
const defaultSchemaFilter = {
  externalTables: [],
  exclude: [],
} satisfies MigrateTypes.SchemaFilter
```

When checking for null/undefined values, be explicit about both:
```typescript
// Handle both null and undefined
if (obj.currentTimeframe == null) {
  return {}
}

// Or check explicitly
if (response.body === null) {
  return reject(new Error('response.body is null'))
}
```

This approach reduces conditional access chains, makes code more predictable, prevents null reference errors, and improves type safety by making the presence or absence of values explicit rather than implicit.