sickn33/agentic-awesome-skills · warning · Error

Data must be an object

Error message

Data must be an object

What it means

Thrown by the throw-based validateUser in fp-refactor when the input is falsy or not an object — the outermost structural guard before field checks. It exists to reject null, undefined, primitives, and array misuse in the 'Before' code the skill refactors away.

Source

Thrown at skills/fp-refactor/SKILL.md:69

- Composing multiple fallible operations is verbose

### Pattern: Synchronous try-catch to Either

#### Before (Imperative)

```typescript
function parseJSON(input: string): unknown {
  try {
    return JSON.parse(input);
  } catch (error) {
    throw new Error(`Invalid JSON: ${error}`);
  }
}

function validateUser(data: unknown): User {
  try {
    if (!data || typeof data !== 'object') {
      throw new Error('Data must be an object');
    }
    const obj = data as Record<string, unknown>;
    if (typeof obj.name !== 'string') {
      throw new Error('Name is required');
    }
    if (typeof obj.age !== 'number') {
      throw new Error('Age must be a number');
    }
    return { name: obj.name, age: obj.age };
  } catch (error) {
    throw error;
  }
}

// Usage with nested try-catch
function processUserInput(input: string): User | null {
  try {
    const data = parseJSON(input);

View on GitHub (pinned to 58d857988f)

Solutions

1. Validate the shape at the boundary with a schema library so non-objects never reach this function
2. Return Either/Result with the reason instead of throwing
3. Add a reusable isRecord(x) type guard shared across validators

Example fix

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

// after
const isRecord = (x: unknown): x is Record<string, unknown> =>
  typeof x === 'object' && x !== null
const validateUser = (data: unknown): E.Either<string, User> =>
  !isRecord(data) ? E.left('Data must be an object') : E.right(data as User)

const isRecord = (x: unknown) => typeof x === 'object' && x !== null && !Array.isArray(x)

const isRecord = (x: unknown): x is Record<string, unknown> =>
  typeof x === 'object' && x !== null

When it happens

Trigger: Calling validateUser(null), validateUser('name=Bob'), validateUser(42), or validateUser(undefined) from an unvalidated request body.

Common situations: Optional request bodies not checked before validation; query-string parsers returning strings; JSON.parse of 'null' producing null; form-encoded endpoints feeding primitives.

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

• Age required
• Age must be a number
• ID required
• Age must be positive
• Name is required

AI-assisted analysis of sickn33/agentic-awesome-skills@58d857988f (2026-08-26). Data as JSON: /api/errors/cc5eb4772e7d331d. Report an issue: GitHub.