fix (potential) problems with empty file_extensions

app/assets/javascripts/exercises.js.erb

@@ -264,7 +264,7 @@ $(document).on('turbolinks:load', function () {
     var inferFileAttributes = function () {
         $(document).on('change', 'input[type="file"]', function () {
             var filename = $(this).val().split(/\\|\//g).pop();
-            var file_extension = '.' + filename.split('.')[1];
+            var file_extension = filename.includes('.') ? '.' + filename.split('.')[1] : '';
             var file_type = findFileTypeByFileExtension(file_extension);
             var name = filename.split('.')[0];
             var parent = $(this).parents('li');

app/models/file_type.rb

@@ -26,7 +26,7 @@ class FileType < ApplicationRecord
   validates :indent_size, presence: true, unless: :binary?
   validates :name, presence: true
   validates :renderable, inclusion: [true, false]
-  validates :file_extension, length: { minimum:0, allow_nil: false}
+  validates :file_extension, length: {minimum: 0, allow_nil: false}
 
   %i[audio compressed csv excel image pdf powerpoint video word].each do |type|
     define_method("#{type}?") do

app/services/proforma_service/convert_task_to_exercise.rb

@@ -101,8 +101,8 @@ module ProformaService
     end
 
     def file_type(extension)
-      FileType.find_or_create_by(file_extension: extension.presence) do |file_type|
+      FileType.find_or_create_by(file_extension: extension) do |file_type|
-        file_type.name = extension[1..]
+        file_type.name = "Imported #{extension}"
         file_type.user = @user
         file_type.indent_size = 4
         file_type.editor_mode = 'ace/mode/plain_text'

spec/services/proforma_service/convert_task_to_exercise_spec.rb

@@ -157,6 +157,24 @@ describe ProformaService::ConvertTaskToExercise do
         expect { convert_to_exercise_service.save! }.to change(Exercise, :count).by(1)
       end
 
+      context 'when file is a Makefile' do
+        let(:filename) { "#{path}Makefile" }
+
+        it 'creates an exercise with a file with a Filetype, that has the correct attributes' do
+          expect(convert_to_exercise_service.files.first).to have_attributes(
+            file_type: be_a(FileType).and(have_attributes(file_extension: '', name: 'Imported'))
+          )
+        end
+
+        context 'when FileType for Makefile exists' do
+          let!(:makefile_filetype) { create(:makefile) }
+
+          it 'creates an exercise with a file with a Filetype, that has the correct attributes' do
+            expect(convert_to_exercise_service.files.first).to have_attributes(file_type: makefile_filetype)
+          end
+        end
+      end
+
       context 'when file is a main_file' do
         let(:meta_data) do
           {