Update NdjsonPipeline#transform to return if data is nil

lib/bulk_imports/ndjson_pipeline.rb

@@ -10,7 +10,12 @@ module BulkImports
       ndjson_pipeline!
 
       def transform(context, data)
+        return unless data
+
         relation_hash, relation_index = data
+
+        return unless relation_hash
+
         relation_definition = import_export_config.top_relation_tree(relation)
 
         relation_object = deep_transform_relation!(relation_hash, relation, relation_definition) do |key, hash|

spec/lib/bulk_imports/ndjson_pipeline_spec.rb

@@ -130,6 +130,22 @@ RSpec.describe BulkImports::NdjsonPipeline do
 
       subject.transform(context, data)
     end
+
+    context 'when data is nil' do
+      before do
+        expect(Gitlab::ImportExport::Group::RelationFactory).not_to receive(:create)
+      end
+
+      it 'returns' do
+        expect(subject.transform(nil, nil)).to be_nil
+      end
+
+      context 'when relation hash is nil' do
+        it 'returns' do
+          expect(subject.transform(nil, [nil, 0])).to be_nil
+        end
+      end
+    end
   end
 
   describe '#load' do