Right now it looks like department is just a single field with one value. How can it hold a List.
You might have a Department table that in the Employee table has a FK id that maps to a record in the Department table. In that case you mappings should be ManyToOne from Employee to Department. but you cna also have a bi-directional association in Department that has a List of Employees.
But it looks like your table design doesn't support that and that your mappings doesn't show that.