If something comes into Tableau as blank or NULL, you can edit the alias, but it will change all of the blanks or nulls to the same name. From what I'm reading, it sounds like you might need to:
1. Do this on the backend... (I'm not sure of your data structure - but you might be able to join with a reference table).
2. The only other thing that might help here is if there is some other identifier on the row to do logic in a calculated field. For example, if you know "XYZ company" is always "TX", you can create a new field that will assign the location for you.
Are you able to share a workbook or an example? If there is sensitive info, you can exclude those columns for this.
You can do that using a Calculated field.. Use the below formula to change you NULL values to the state you want to reffer...(change Others as the state name you want)
With the original Fields.. create the Map.. click on the 1 unknown ... Then Edit location..
Then just drag the Calculated filed to the color shelf .. so that all the states will have the correct name.. including the NULL.
Check the attached workbook.. Thank you!!
State Null.twbx 44.0 KB