user: Question: What is the transfer window with n/a as the Transfer fee, Free Agent for the Moving to, and Joe Sagar as the name?
Columns: ['Nat.', 'Name', 'Moving to', 'Type', 'Transfer window', 'Transfer fee']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['SCO', 'Martin Ure', "Queen's Park", 'End of contract', 'Summer', 'n/a']
SQL:

assistant: SELECT "Transfer window" FROM "Table" WHERE "Transfer fee" = 'n/a' AND "Moving to" = 'Free Agent' AND "Name" = 'Joe Sagar';