Multiple issue assignee: fix for CE restrictions

app/services/issues/base_service.rb

@@ -25,7 +25,7 @@ module Issues
       return if params[:assignee_ids].blank?
 
       # The number of assignees is limited by one for GitLab CE
-      params[:assignee_ids].slice!(0, 1)
+      params[:assignee_ids] = params[:assignee_ids][0, 1]
 
       assignee_ids = params[:assignee_ids].select { |assignee_id| assignee_can_read?(issuable, assignee_id) }
 

spec/services/issues/update_service_spec.rb

@@ -40,7 +40,7 @@ describe Issues::UpdateService, services: true do
         {
           title: 'New title',
           description: 'Also please fix',
-          assignee_ids: [user2.id, user3.id],
+          assignee_ids: [user2.id],
           state_event: 'close',
           label_ids: [label.id],
           due_date: Date.tomorrow
@@ -53,7 +53,7 @@ describe Issues::UpdateService, services: true do
         expect(issue).to be_valid
         expect(issue.title).to eq 'New title'
         expect(issue.description).to eq 'Also please fix'
-        expect(issue.assignees).to match_array([user2, user3])
+        expect(issue.assignees).to match_array([user2])
         expect(issue).to be_closed
         expect(issue.labels).to match_array [label]
         expect(issue.due_date).to eq Date.tomorrow