user: Question: What country is the player, with an Undisclosed transfer fee and moving to Nacional, from?
Columns: ['Name', 'Country', 'Status', 'Moving to', 'Transfer window', 'Transfer fee']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Ujkani', 'ALB BEL', 'Transferred', 'Palermo', 'Summer', 'Undisclosed']
SQL:

assistant: SELECT "Country" FROM "Table" WHERE "Transfer fee" = 'Undisclosed' AND "Moving to" = 'Nacional';