sickn33/agentic-awesome-skills · error · Error

Must be object

Error message

Must be object

What it means

First guard of the multi-check validateUser example in the fp-pragmatic skill (skills/fp-pragmatic/SKILL.md:465). Thrown when the raw input is falsy or not an object: the shape check that must pass before any field can be safely read. The doc replaces this throw-on-first-error style with an error-accumulating Either version.

Source

Thrown at skills/fp-pragmatic/SKILL.md:465

    O.flatMap(m => O.fromNullable(m.email))
  )

// Use it
pipe(
  getManagerEmail(employee),
  O.fold(
    () => sendToDefault(),
    (email) => sendTo(email)
  )
)
```

### Validation with Multiple Checks

```typescript
// Before: Throws on first error
function validateUser(data: unknown): User {
  if (!data || typeof data !== 'object') throw new Error('Must be object')
  const obj = data as Record<string, unknown>
  if (typeof obj.email !== 'string') throw new Error('Email required')
  if (!obj.email.includes('@')) throw new Error('Invalid email')
  if (typeof obj.age !== 'number') throw new Error('Age required')
  if (obj.age < 0) throw new Error('Age must be positive')
  return obj as User
}

// After: Returns first error, type-safe
const validateUser = (data: unknown): E.Either<string, User> =>
  pipe(
    E.Do,
    E.bind('obj', () =>
      typeof data === 'object' && data !== null
        ? E.right(data as Record<string, unknown>)
        : E.left('Must be object')
    ),
    E.bind('email', ({ obj }) =>

View on GitHub (pinned to 58d857988f)

Solutions

1. Parse and validate the payload shape at the boundary with a schema library (zod, io-ts, valibot) before it reaches domain code
2. Use the doc AFTER pattern: return Either with accumulated errors instead of throwing on the first failed check
3. Reject non-object bodies early in the HTTP layer with a 400 and a clear message

Example fix

// before
if (!data || typeof data !== 'object') throw new Error('Must be object')

// after
const isRecord = (u: unknown): u is Record<string, unknown> =>
  typeof u === 'object' && u !== null && !Array.isArray(u)
if (!isRecord(data)) return E.left(['Must be object'])

if (typeof data !== 'object' || data === null || Array.isArray(data)) {
  return badRequest('body must be a JSON object')
}

const isRecord = (u: unknown): u is Record<string, unknown> =>
  typeof u === 'object' && u !== null && !Array.isArray(u)

When it happens

Trigger: Calling validateUser with null, undefined, a string, a number, or an array: anything where typeof data is not object or data is null.

Common situations: JSON.parse of an empty or malformed request body producing null; query-string params arriving as strings; arrays passing the typeof check but failing later field checks; API consumers sending scalars where objects are expected.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• Invalid range "${t}" in ${fieldDef.name}
• Value ${v} out of range for ${fieldDef.name} (${fieldDef.min
• Range ${lo}-${hi} out of bounds for ${fieldDef.name} (${fiel
• Expected 5 fields (got ${parts.length}). Format: minute hour
• ID required

AI-assisted analysis of sickn33/agentic-awesome-skills@58d857988f (2026-08-26). Data as JSON: /api/errors/4eb3a9db73945a79. Report an issue: GitHub.