Add controller and feature specs

Also optimizes the target service so that we don't do a useless query

app/services/quick_actions/target_service.rb

@@ -17,12 +17,16 @@ module QuickActions
 
     # rubocop: disable CodeReuse/ActiveRecord
     def issue(type_id)
+      return project.issues.build if type_id.nil?
+
       IssuesFinder.new(current_user, project_id: project.id).find_by(iid: type_id) || project.issues.build
     end
     # rubocop: enable CodeReuse/ActiveRecord
 
     # rubocop: disable CodeReuse/ActiveRecord
     def merge_request(type_id)
+      return project.merge_requests.build if type_id.nil?
+
       MergeRequestsFinder.new(current_user, project_id: project.id).find_by(iid: type_id) || project.merge_requests.build
     end
     # rubocop: enable CodeReuse/ActiveRecord

ee/app/controllers/groups/epics_controller.rb

@@ -20,7 +20,9 @@ class Groups::EpicsController < Groups::ApplicationController
     push_frontend_feature_flag(:vue_issuable_epic_sidebar, @group)
   end
 
-  def new; end
+  def new
+    @noteable = Epic.new
+  end
 
   def index
     @epics = @issuables

ee/app/services/ee/quick_actions/target_service.rb

@@ -14,6 +14,9 @@ module EE
       # rubocop: disable CodeReuse/ActiveRecord
       def epic(type_id)
         group = params[:group]
+
+        return group.epics.build if type_id.nil?
+
         EpicsFinder.new(current_user, group_id: group.id).find_by(iid: type_id) || group.epics.build
       end
       # rubocop: enable CodeReuse/ActiveRecord

ee/app/views/groups/epics/new.html.haml

 - @gfm_form = true
-- @noteable = Epic.new
 - add_to_breadcrumbs _("Epics"), group_epics_path(@group)
 - breadcrumb_title _("New")
 - page_title _("New epic")

ee/changelogs/unreleased/add-support-for-epic-descriptions-quick-actions-on-epic-creation-form.yml

+---
+title: Fix quick actions autocomplete in new epic form
+merge_request: 37099
+author:
+type: fixed

ee/spec/controllers/groups/autocomplete_sources_controller_spec.rb

@@ -105,5 +105,17 @@ RSpec.describe Groups::AutocompleteSourcesController do
         }
       )
     end
+
+    it 'handles new epics' do
+      get :commands, params: { group_id: group, type: 'Epic', type_id: nil }
+
+      expect(json_response).to be_an(Array)
+      expect(json_response).to include(
+        {
+          'name' => 'cc', 'aliases' => [], 'description' => 'CC',
+          'params' => ['@user'], 'warning' => '', 'icon' => ''
+        }
+      )
+    end
   end
 end