Rules Hack - Dropdown list as identifier

In Rules Action, if we are to use a drop-down or (multi-select dropdown) list as an identifer and if nulls are expected from the source,
- everytime a new record is created when the dropdown list is null (since null is not equal to null)
- if we have to use any of the existing dropdown list values as a default value - we are prone to show erroneous data.

Hack: In the MDA dropdown list, create a dummy value 'NA' - this can be used as the default value and no nulls would be populated.