Fix issuable import csv base service

- Raise CSV error if files have no lines
- Add specs for empty file case

app/services/issuable/import_csv/base_service.rb

@@ -38,7 +38,7 @@ module Issuable
 
       def with_csv_lines
         csv_data = @csv_io.open(&:read).force_encoding(Encoding::UTF_8)
-        verify_headers!(csv_data)
+        validate_headers_presence!(csv_data.lines.first)
 
         csv_parsing_params = {
           col_sep: detect_col_sep(csv_data.lines.first),
@@ -49,9 +49,9 @@ module Issuable
         CSV.new(csv_data, csv_parsing_params).each.with_index(2)
       end
 
-      def verify_headers!(data)
-        headers = data.lines.first.downcase
-        return if headers.include?('title') && headers.include?('description')
+      def validate_headers_presence!(headers)
+        headers.downcase! if headers
+        return if headers && headers.include?('title') && headers.include?('description')
 
         raise CSV::MalformedCSVError
       end

changelogs/unreleased/246857-fix-issuable-import-csv-service.yml

+---
+title: Fix error in Issuable::ImportCsv::BaseService when CSV file is empty
+merge_request: 47918
+author:
+type: fixed

spec/support/services/issuable_import_csv_service_shared_examples.rb

@@ -26,29 +26,33 @@ RSpec.shared_examples 'issuable import csv service' do |issuable_type|
     end
   end
 
+  shared_examples_for 'invalid file' do
+    it 'returns invalid file error' do
+      expect(subject[:success]).to eq(0)
+      expect(subject[:parse_error]).to eq(true)
+    end
+
+    it_behaves_like 'importer with email notification'
+    it_behaves_like 'an issuable importer'
+  end
+
   describe '#execute' do
-    context 'invalid file' do
+    context 'invalid file extension' do
       let(:file) { fixture_file_upload('spec/fixtures/banana_sample.gif') }
 
-      it 'returns invalid file error' do
-        expect(subject[:success]).to eq(0)
-        expect(subject[:parse_error]).to eq(true)
-      end
+      it_behaves_like 'invalid file'
+    end
 
-      it_behaves_like 'importer with email notification'
-      it_behaves_like 'an issuable importer'
+    context 'empty file' do
+      let(:file) { fixture_file_upload('spec/fixtures/csv_empty.csv') }
+
+      it_behaves_like 'invalid file'
     end
 
     context 'file without headers' do
       let(:file) { fixture_file_upload('spec/fixtures/csv_no_headers.csv') }
 
-      it 'returns invalid file error' do
-        expect(subject[:success]).to eq(0)
-        expect(subject[:parse_error]).to eq(true)
-      end
-
-      it_behaves_like 'importer with email notification'
-      it_behaves_like 'an issuable importer'
+      it_behaves_like 'invalid file'
     end
 
     context 'with a file generated by Gitlab CSV export' do