Updated based on Ruby feedback

app/helpers/issuables_helper.rb

@@ -47,7 +47,7 @@ module IssuablesHelper
     end
   end
-  def milestone_dropdown_label(milestone_title, default_label)
+  def milestone_dropdown_label(milestone_title, default_label = "Milestone")
     if milestone_title == Milestone::Upcoming.name
       milestone_title = Milestone::Upcoming.title
     end

app/views/shared/issuable/_milestone_dropdown.html.haml

 - if params[:milestone_title]
   = hidden_field_tag(:milestone_title, params[:milestone_title])
-= dropdown_tag(milestone_dropdown_label(params[:milestone_title], "Milestone"), options: { title: "Filter by milestone", toggle_class: 'js-milestone-select js-filter-submit', filter: true, dropdown_class: "dropdown-menu-selectable",
+= dropdown_tag(milestone_dropdown_label(params[:milestone_title]), options: { title: "Filter by milestone", toggle_class: 'js-milestone-select js-filter-submit', filter: true, dropdown_class: "dropdown-menu-selectable",
   placeholder: "Search milestones", footer_content: @project.present?, data: { show_no: true, show_any: true, show_upcoming: true, field_name: "milestone_title", selected: params[:milestone_title], project_id: @project.try(:id), milestones: milestones_filter_dropdown_path, default_label: "Milestone" } }) do
   - if @project
     %ul.dropdown-footer-list

spec/features/issues/filter_by_milestone_spec.rb

@@ -11,7 +11,7 @@ feature 'Issue filtering by Milestone', feature: true do
     visit_issues(project)
     filter_by_milestone(Milestone::None.title)
-    expect(page).to have_css('.issue .title', count: 1)
+    expect(page).to have_css('.issue', count: 1)
   end
   context 'filters by upcoming milestone', js: true do
@@ -22,7 +22,7 @@ feature 'Issue filtering by Milestone', feature: true do
       visit_issues(project)
       filter_by_milestone(Milestone::Upcoming.title)
-      expect(page).to have_css('.issue .title', count: 0)
+      expect(page).to have_css('.issue', count: 0)
     end
     it 'should show issues in future' do

spec/features/merge_requests/filter_by_milestone_spec.rb

@@ -11,7 +11,7 @@ feature 'Merge Request filtering by Milestone', feature: true do
     visit_merge_requests(project)
     filter_by_milestone(Milestone::None.title)
-    expect(page).to have_css('.merge-request-title', count: 1)
+    expect(page).to have_css('.merge-request', count: 1)
   end
   context 'filters by upcoming milestone', js: true do
@@ -22,7 +22,7 @@ feature 'Merge Request filtering by Milestone', feature: true do
       visit_merge_requests(project)
       filter_by_milestone(Milestone::Upcoming.title)
-      expect(page).to have_css('.merge-request-title', count: 0)
+      expect(page).to have_css('.merge-request', count: 0)
     end
     it 'should show issues in future' do