DropDownChoice and null value internationalization key

[Guillaume Mary]

Hi all,

The DropDownChoice and overall AbstractSingleSelectChoice does not allow to 
specify the internationalization key for null nor nullValid values.
Instead it laies down the management of those keys with getId() + ".null".

I suggest a very small enhancement to externalize the building of these keys in 
2 protected methods getNullKey() and getNullValidKey() (the names don't really 
matter) and call them in the 
AbstractSingleSelectChoice.getDefaultChoice(Object) method.

It won't disturb the actual running and allows developper to organize their 
keys as they like in order to help translators know what keys are about (with 
prefix for example). For now this is not possible, or we have to change 
component ids ...


Here are the 2 methods :
protected String getNullValidKey() {
                               return getId() + ".nullValid";
                }

                protected String getNullKey() {
                               return getId() + ".null";
                }


If ok, I can create a JIRA enhancement with the full patch.

Thanks