investigate and fix empty strings for setting

[opsaaaaa]

find any setting that can be saved as empty strings
write a concern use_nil_for_blank on before_save replace the problematic settings that are blank with nil.
write a rake task to find all settings that are empty strings and replace them with strings.

we may decide to refactor the settings into a new model or a new column. if so this should be handled at the same time.