Add Null Source for Dictionaries

Why it matters

This feature allows users to create dictionaries with a Null source, which effectively provides an empty dictionary. It is useful for scenarios where a dictionary definition is required but no actual data source is available or needed, enabling simpler configuration and avoiding errors.

How to use it

To use the Null source dictionary, define the dictionary with source = Null in the dictionary configuration. This will create an empty dictionary that can be used as a placeholder or for testing.