# TypeError: argument of type 'NoneType' is not iterable

- **ID:** `python/fastapi-typeerror-argument-of-type-is-not-iterable`
- **Domain:** python
- **Category:** type_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

Trying to iterate over a variable that is None, often from a query parameter or dependency that returns None.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.x | active | — | — |

## Workarounds

1. **Check for None before iterating** (95% success)
   ```
   if items is not None:
    for item in items: pass
   ```
2. **Provide default empty list** (90% success)
   ```
   items = request.query_params.get('items', [])
   ```

## Dead Ends

- **Assuming all parameters are always provided** — Optional parameters can be None if not provided. (70% fail)
- **Using for loop without checking None** — None is not iterable. (90% fail)