# using HTML value
field :password, as: :password, help: 'You may verify the password strength <a href="http://www.passwordmeter.com/">here</a>.'
```

<Image src="/assets/img/fields-reference/help-text.png" width="954" height="271" alt="Help text" />

## Nullable

When a user uses the **Save** button, Avo stores the value for each field in the database. However, there are cases where you may prefer to explicitly instruct Avo to store a `NULL` value in the database row when the field is empty. You do that by using the `nullable` option, which converts `nil` and empty values to `NULL`.

You may also define which values should be interpreted as `NULL` using the `null_values` method.

```ruby