typescript.missing_null_check

Correctness High

Detects potential null/undefined access without proper checks.

Why It Matters

Missing null checks:

• Runtime crashes — “Cannot read property of undefined”
• Silent failures — Undefined propagates through code
• User-facing errors — Unhandled exceptions break UX

Example

// ❌ Before (no null check)
function getUserName(user: User | null): string {
  return user.name; // Crashes if user is null!
}

// ✅ After (with null check)
function getUserName(user: User | null): string {
  if (!user) {
    throw new Error('User is required');
  }
  return user.name;
}

// Or with optional chaining:
function getUserName(user: User | null): string | undefined {
  return user?.name;
}

// Or with nullish coalescing:
function getUserName(user: User | null): string {
  return user?.name ?? 'Anonymous';
}

What Unfault Detects

• Property access on nullable types
• Missing null guards before access
• Unsafe type assertions

Auto-Fix

Unfault can add optional chaining or null checks.

Related Rules

• typescript.unsafe_any