Make the Label field nullable in the TranslatedResourceOfX Types

[gmiserez]

Describe the solution you'd like
Make the Label field nullable in the TranslatedResourceOfX Types.
The value of the value field should be null when no translation was returned by the IResourcesProvider.

Describe alternatives you've considered
Currently, the Label field returns a string representation of the key when no translation is found. This makes it hard to track missing resources, in the absence of any Observer-like Feature to track events occuring during translations.

Additional context
Add any other context or screenshots about the feature request here.