Rails 4 strong params error: no implicit conversion of Symbol into String

I am importing the data from a spreadsheet to the app database.

The data is parsed by rows. Each parsed row looks like:

{:department=>{:school=>"Graduate School of Business", :name=>"Graduate
School of Business", :program=>"MBA Program",
:url=>"http://www.gsb.stanford.edu/mba", :intro=>"The Stanford MBA
Program is a two-year, full-time, residential program.",
:students_number=>"Approximately 80 annually",
:students_with_aids_number=>nil, :gre_scroe=>nil, :toefl_score=>nil,
:world_rank=>nil, :us_rank=>nil, :without_aid_deadline=>nil,
:with_aid_deadline=>nil, :salary=>nil, :institute_id=>1}}

To create a department:

# att is the hash shown above
    department = Department.new(department_params(att))
    if !department.save
        puts "Error: \n department can't be save:
#{department.errors.full_messages}"
    end

def department_params params
   params.require(:department).permit(:name,:url,:institute_id)
end

But I got the error:

no implicit conversion of Symbol into String
which points to

params.require(:department).permit(:name,:url,:institute_id)

How could I fix it? Thanks!