FixNum problem

def get_end_customers(client_id="")
  if params[:client_id].nil?
    @client_id = client_id
  else
    @client_id = params[:client_id]
  end
  unless @client_id.nil? || @client_id.empty? #this line breaks when @client_id is FixNum type
    #do something
  end
end