Fix merge request creation without branch selected

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/services/merge_requests/build_service.rb

@@ -12,8 +12,13 @@ module MergeRequests
       merge_request.target_project ||= (project.forked_from_project || project)
       merge_request.target_branch ||= merge_request.target_project.default_branch
 
-      unless merge_request.target_branch && merge_request.source_branch
-        return build_failed(merge_request, nil)
+      if merge_request.target_branch.blank? || merge_request.source_branch.blank?
+        message =
+          if params[:source_branch] || params[:target_branch]
+            "You must select source and target branch"
+          end
+
+        return build_failed(merge_request, message)
       end
 
       compare_result = CompareService.new.execute(

spec/services/merge_requests/merge_service_spec.rb

@@ -24,11 +24,6 @@ describe MergeRequests::MergeService do
       it { expect(merge_request).to be_valid }
       it { expect(merge_request).to be_merged }
 
-      it 'should execute hooks with merge action' do
-        expect(service).to have_received(:execute_hooks).
-                               with(merge_request, 'merge')
-      end
-
       it 'should send email to user2 about merge of new merge_request' do
         email = ActionMailer::Base.deliveries.last
         expect(email.to.first).to eq(user2.email)