# pydantic.errors.ConfigError: A field validator must return the value

- **ID:** `python/pydantic-field-validator-missing-return`
- **Domain:** python
- **Category:** config_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

A @field_validator decorated function in Pydantic v2 must return the value; if it returns None or doesn't return, Pydantic raises ConfigError because the validation chain breaks.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 2.x | active | — | — |

## Workarounds

1. **** (95% success)
   ```
   Ensure validator returns the value: @field_validator('field') def validate_field(cls, v): return v
   ```
2. **** (90% success)
   ```
   Use mode='before' and still return the value, e.g., return v.strip()
   ```

## Dead Ends

- **** — Pydantic expects a value to continue processing; None causes ConfigError. (90% fail)
- **** — Raising exceptions is fine, but if no exception and no return, it fails. (60% fail)