```
@Retention(RUNTIME)
@Target({FIELD,TYPE})
public @interface PreserveNotNull
```
On a field: indicates that, when converting a config to a java object, the value of the field must not be overriden by a null value from the config. Only non-null config values can replace the field's value.
On a class declaration: applies the effect of this annotation to all the fields.

Annotation Type PreserveNotNull