Fixes issue with dropdowns not selecting values

Fixes issue with dropdowns not selecting when navigating between tabs

Closes #14813

app/assets/javascripts/gl_dropdown.js.coffee

@@ -318,6 +318,8 @@ class GitLabDropdown
             input = $(input)
                       .attr('id', @options.inputId)
           @dropdown.before input
+        else
+          field.val value
 
       return selectedObject
 

app/assets/javascripts/milestone_select.js.coffee

@@ -84,12 +84,16 @@ class @MilestoneSelect
 
           # display:block overrides the hide-collapse rule
           $value.removeAttr('style')
-        clicked: (e) ->
+        clicked: (selected) ->
           if $dropdown.hasClass 'js-filter-bulk-update'
             return
 
-          if $dropdown.hasClass 'js-filter-submit'
-            $dropdown.parents('form').submit()
+          if $dropdown.hasClass('js-filter-submit')
+            if selected.name?
+              selectedMilestone = selected.name
+            else
+              selectedMilestone = ''
+            Issues.filterResults $dropdown.closest('form')
           else
             selected = $selectbox
               .find('input[type="hidden"]')

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

@@ -7,13 +7,13 @@
             class: "check_all_issues left"
       .issues-other-filters
         .filter-item.inline
-          - if params[:author_id]
+          - if params[:author_id].present?
             = hidden_field_tag(:author_id, params[:author_id])
           = dropdown_tag(user_dropdown_label(params[:author_id], "Author"), options: { toggle_class: "js-user-search js-filter-submit js-author-search", title: "Filter by author", filter: true, dropdown_class: "dropdown-menu-user dropdown-menu-selectable dropdown-menu-author js-filter-submit",
             placeholder: "Search authors", data: { any_user: "Any Author", first_user: (current_user.username if current_user), current_user: true, project_id: (@project.id if @project), selected: params[:author_id], field_name: "author_id", default_label: "Author" } })
 
         .filter-item.inline
-          - if params[:assignee_id]
+          - if params[:assignee_id].present?
             = hidden_field_tag(:assignee_id, params[:assignee_id])
           = dropdown_tag(user_dropdown_label(params[:assignee_id], "Assignee"), options: { toggle_class: "js-user-search js-filter-submit js-assignee-search", title: "Filter by assignee", filter: true, dropdown_class: "dropdown-menu-user dropdown-menu-selectable dropdown-menu-assignee js-filter-submit",
             placeholder: "Search assignee", data: { any_user: "Any Assignee", first_user: (current_user.username if current_user), null_user: true, current_user: true, project_id: (@project.id if @project), selected: params[:assignee_id], field_name: "assignee_id", default_label: "Assignee" } })

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

-- if params[:label_name]
+- if params[:label_name].present?
   = hidden_field_tag(:label_name, params[:label_name])
 .dropdown
   %button.dropdown-menu-toggle.js-label-select.js-filter-submit{type: "button", data: {toggle: "dropdown", field_name: "label_name", show_no: "true", show_any: "true", selected: params[:label_name], project_id: @project.try(:id), labels: labels_filter_path, default_label: "Label"}}

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

-- if params[:milestone_title]
+- if params[:milestone_title].present?
   = hidden_field_tag(:milestone_title, params[:milestone_title])
 = 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