Create Two option values in existing crm

I had created a 2 option values (field: hasorignaldatetime)in my existing Case's form, & had set the default value to 'No'.

If I perform an advance find, existing cases prior to this 2 option values creation, the 'hasorignaldatetime ' will be empty.

So I would like to ask in my plugin, how do I perform a condition check on this field?  Is an empty hasorignaldatetime equivalent to 'false'?

Or perhaps I need to check for null in Boolean?  

Thanks.