Github user sjcorbett commented on the pull request:
https://github.com/apache/incubator-brooklyn/pull/356#issuecomment-64686894
I'd argue it does simplify the code. It is not only preventing `set(null)`,
it also provides a standard way to catch missing configuration when an entity
is created. Currently, to check a ConfigKey was set you have to write something
like:
```
@Override
public void init() {
checkNotNull(getConfig(MY_CONFIG), "Entity requires a value for
MY_CONFIG");
}
```
This splits the statement of intent that a value for `MY_CONFIG` must be
set when the entity is created away from definition of the key. There is no
feasible way for us to generate documentation that indicates that `MY_CONFIG`
must be set.
With the change in this pull request we can replace the check in the `init`
method by defining the config key as:
```
ConfigKey<Object> MY_CONFIG = ConfigKeys.newConfigKey(Object.class)
.nonNull()
.build();
```
Attempts to create entities missing mandatory configuration are
automatically caught in `InternalEntityFactory`. We can extend the jsgui to
indicate required configuration when you're adding an app or an entity (and
even prevent submissions that are missing such values) or are browsing the
catalogue. We can also indicate required configuration in the catalogue
documentation on the Brooklyn website.
The change is backwards compatible - all existing ConfigKeys remain
nullable. The nulling-a-parents-key case is valid. I envisage this being used
selectively rather than left, right and centre.
It should definitely be annotated `@Beta`.
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