Fix creating issue in milestone list

Changelog: fixed
EE: true

app/assets/javascripts/boards/boards_util.js

@@ -108,7 +108,8 @@ export function formatIssueInput(issueInput, boardConfig) {
 
   return {
     ...issueInput,
-    milestoneId: milestoneId ? fullMilestoneId(milestoneId) : null,
+    milestoneId:
+      milestoneId && milestoneId !== -1 ? fullMilestoneId(milestoneId) : issueInput.milestoneId,
     labelIds: [...labelIds, ...(labels?.map((l) => fullLabelId(l)) || [])],
     assigneeIds: [...assigneeIds, ...(assigneeId ? [fullUserId(assigneeId)] : [])],
   };

ee/spec/features/boards/new_issue_spec.rb

@@ -3,10 +3,17 @@
 require 'spec_helper'
 
 RSpec.describe 'Issue Boards new issue', :js do
-  let_it_be(:user)         { create(:user) }
-  let_it_be(:project)      { create(:project, :public) }
-  let_it_be(:board)        { create(:board, project: project) }
-  let_it_be(:backlog_list) { create(:backlog_list, board: board) }
+  before do
+    stub_licensed_features(board_milestone_lists: true)
+  end
+
+  let_it_be(:user)            { create(:user) }
+  let_it_be(:project)         { create(:project, :public) }
+  let_it_be(:milestone)       { create(:milestone, project: project, title: 'Milestone 1') }
+  let_it_be(:board)           { create(:board, project: project) }
+  let_it_be(:backlog_list)    { create(:backlog_list, board: board) }
+
+  let!(:milestone_list)       { create(:milestone_list, board: board, milestone: milestone, position: 0) }
 
   context 'authorized user' do
     before do
@@ -17,7 +24,7 @@ RSpec.describe 'Issue Boards new issue', :js do
       visit project_board_path(project, board)
       wait_for_requests
 
-      expect(page).to have_selector('.board', count: 2)
+      expect(page).to have_selector('.board', count: 3)
     end
 
     it 'successfully assigns weight to newly-created issue' do
@@ -48,5 +55,32 @@ RSpec.describe 'Issue Boards new issue', :js do
         expect(find('.board-card-weight .board-card-info-text').text).to eq("10")
       end
     end
+
+    describe 'milestone list' do
+      it 'successfuly loads milestone to be added to newly created issue' do
+        page.within(all('.board')[1]) do
+          click_button 'New issue'
+        end
+
+        page.within(first('.board-new-issue-form')) do
+          find('.form-control').set('new issue')
+          click_button 'Create issue'
+        end
+
+        wait_for_requests
+
+        page.within(all('.board')[1]) do
+          find('.board-card').click
+        end
+
+        page.within('[data-testid="sidebar-milestones"]') do
+          click_button 'Edit'
+
+          wait_for_requests
+
+          expect(page).to have_content 'Milestone 1'
+        end
+      end
+    end
   end
 end