Estoy intentando probar mi aplicación y continuamente aparece el siguiente error:

Error:
    ContractsControllerTest#test_should_get_show:
    ActiveRecord::Fixture::FormatError: ActiveRecord::Fixture::FormatError

Error:
    ContractsControllerTest#test_should_get_show:
    NoMethodError: undefined method `each' for nil:NilClass

A continuación se muestra el código en mi controlador de contrato y tengo un código similar como este en todos los controladores.

    def index
      @contract = Contract.all.paginate(page: params[:page], :per_page => 70) 
    end


    def show
      @contract = Contract.find(params[:id])

    end



    def new
       @contract = Contract.new
    end


    def create
         @contract = Contract.new(located)
        if  @contract.save
            flash[:success] = "A record has been successfully added"
        redirect_to contracts_path
        else
          render 'new'
        end
    end



    def located
       params.require(:contract).permit(:contract_name, :contract_status, :services_rendered, :contract_value, :award_year)
    end


       # editing  a record in the contract from cotract table 
     def edit
        @contract = Contract.find(params[:id])
     end





      def update
        @contract = Contract.find(params[:id])
        if @contract.update_attributes(located)
           flash[:success] = "Contract form updated"
           redirect_to contracts_path
        else
           render'edit'
        end
      end



    def destroy
        Contract.find(params[:id]).destroy
        flash[:success] = "A record has been successfully deleted"
        redirect_to contracts_path
    end

A continuación se muestra el seguimiento completo del error cuando ejecuto el comando rails db: fixtures: load --trace

rails aborted!
ActiveRecord::Fixture::FormatError: ActiveRecord::Fixture::FormatError
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-      
5.0.5/lib/active_record/fixture_set/file.rb:72:in `validate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-  
5.0.5/lib/active_record/fixture_set/file.rb:49:in `raw_rows'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-    
5.0.5/lib/active_record/fixture_set/file.rb:37:in `config_row'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-
5.0.5/lib/active_record/fixture_set/file.rb:27:in `model_class'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-
5.0.5/lib/active_record/fixtures.rb:791:in `block (2 levels) in    
read_fixture_files'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-   
5.0.5/lib/active_record/fixture_set/file.rb:15:in `open'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-   
5.0.5/lib/active_record/fixtures.rb:790:in `block in read_fixture_files'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord- 
5.0.5/lib/active_record/fixtures.rb:789:in `each'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-
5.0.5/lib/active_record/fixtures.rb:789:in `each_with_object'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-
5.0.5/lib/active_record/fixtures.rb:789:in `read_fixture_files'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-   
5.0.5/lib/active_record/fixtures.rb:598:in `initialize'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-
5.0.5/lib/active_record/fixtures.rb:529:in `new'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-   
5.0.5/lib/active_record/fixtures.rb:529:in `block (2 levels) in     
create_fixtures'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-  
5.0.5/lib/active_record/fixtures.rb:526:in `map'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-
5.0.5/lib/active_record/fixtures.rb:526:in `block in create_fixtures'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-
 5.0.5/lib/active_record/connection_adapters/postgresql/referential_integrity.rb:    22:in `disable_referential_integrity'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-
5.0.5/lib/active_record/fixtures.rb:523:in `create_fixtures'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord- 
5.0.5/lib/active_record/railties/databases.rake:207:in `block (3 levels) in   
<top        (required)>'
/usr/local/rvm/gems/ruby-2.3.0/gems/railties-
5.0.5/lib/rails/commands/rake_proxy.rb:14:in `block in run_rake_task'
/usr/local/rvm/gems/ruby-2.3.0/gems/railties-
5.0.5/lib/rails/commands/rake_proxy.rb:11:in `run_rake_task'
/usr/local/rvm/gems/ruby-2.3.0/gems/railties- 
5.0.5/lib/rails/commands/commands_tasks.rb:51:in `run_command!'
/usr/local/rvm/gems/ruby-2.3.0/gems/railties-
5.0.5/lib/rails/commands.rb:18:in `<top (required)>'
/home/ubuntu/workspace/final_project/bin/rails:9:in `require'
/home/ubuntu/workspace/final_project/bin/rails:9:in `<top (required)>'
/usr/local/rvm/gems/ruby-2.3.0/gems/spring- 
2.0.2/lib/spring/client/rails.rb:28:in `load'
/usr/local/rvm/gems/ruby-2.3.0/gems/spring-
2.0.2/lib/spring/client/rails.rb:28:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/spring-
2.0.2/lib/spring/client/command.rb:7:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/spring-2.0.2/lib/spring/client.rb:30:in    
`run'
/usr/local/rvm/gems/ruby-2.3.0/gems/spring-2.0.2/bin/spring:49:in `<top 
(required)>'
/usr/local/rvm/gems/ruby-2.3.0/gems/spring-    
2.0.2/lib/spring/binstub.rb:31:in `load'
 /usr/local/rvm/gems/ruby-2.3.0/gems/spring-
2.0.2/lib/spring/binstub.rb:31:in`<top (required)>'
/home/ubuntu/workspace/final_project/bin/spring:15:in `require'
/home/ubuntu/workspace/final_project/bin/spring:15:in `<top (required)>'
bin/rails:3:in `load'
bin/rails:3:in `<main>'
Tasks: TOP => db:fixtures:load
(See full trace by running task with --trace)

Mi aplicación contiene 12 controladores, el mismo error ocurre en cada uno de los controladores. Además, tengo 10 tablas en mi esquema, algunas de las cuales contienen referencias / relaciones entre sí.

Realmente no sé qué está mal y he estado luchando con este problema durante aproximadamente cuatro días. Estaría agradecido si alguien pudiera ayudarme con algún código o información que pudiera ayudarme a rastrear la fuente del error. También le agradecería si pudiera proporcionar información sobre exactamente dónde debería colocar el código para rastrear y resolver este error.

Gracias