# E4167

Default implementation is not marked with `= _`.

## Erroneous example

```{literalinclude} /sources/error_codes/4167_error/top.mbt
:language: moonbit
```

## Suggestion

Add `= _` to the methods that have default implementations.

```{literalinclude} /sources/error_codes/4167_fixed/top.mbt
:language: moonbit
:end-at: }
```