DS 1.4 Component Property Type Annotations: Allow elements which only optionally create component properties

[kwin]

Although https://docs.osgi.org/specification/osgi.cmpn/7.0.0/service.component.html#service.component-component.property.value.coercion states

If there is no corresponding component property for a component property type method, the component property type method must:
...
Return null for String, Class, and enum.

This behaviour cannot be leveraged with annotations used on components. So if you want to use the annotation to express a specific component property to be either a String or not set at all, you cannot do that with an element of an already existing annotation (as JLS does not allow null as default value)

For a concrete use case look at https://issues.apache.org/jira/browse/SLING-2938?focusedCommentId=17199448&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-17199448

[kwin]

Currently it states

For component property type methods with a value of an empty array, a property element must not be generated.
(https://docs.osgi.org/specification/osgi.cmpn/7.0.0/service.component.html#service.component-ordering.generated.properties).

Would be nice to extend that to

For component property type methods with a value of an empty array or an empty string, a property element must not be generated.