Use select2 placeholder instead of blank option

app/views/projects/merge_requests/_new_compare.html.haml

@@ -10,7 +10,7 @@
         .panel-body
           = f.select(:source_project_id, [[@merge_request.source_project_path,@merge_request.source_project.id]] , {}, { class: 'source_project select2 span3', disabled: @merge_request.persisted?, required: true })
            
-          = f.select(:source_branch, @merge_request.source_branches, { include_blank: "Select branch" }, {class: 'source_branch select2 span2', required: true})
+          = f.select(:source_branch, @merge_request.source_branches, { include_blank: true }, { class: 'source_branch select2 span2', required: true, data: { placeholder: "Select source branch" } })
         .panel-footer
           .mr_source_commit
 
@@ -22,7 +22,7 @@
           - projects =  @project.forked_from_project.nil? ? [@project] : [@project, @project.forked_from_project]
           = f.select(:target_project_id, options_from_collection_for_select(projects, 'id', 'path_with_namespace', f.object.target_project_id), {}, { class: 'target_project select2 span3', disabled: @merge_request.persisted?, required: true })
            
-          = f.select(:target_branch, @merge_request.target_branches, { include_blank: "Select branch" }, {class: 'target_branch select2 span2', required: true})
+          = f.select(:target_branch, @merge_request.target_branches, { include_blank: true }, { class: 'target_branch select2 span2', required: true, data: { placeholder: "Select target branch" } })
         .panel-footer
           .mr_target_commit
 

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

@@ -25,7 +25,7 @@
         none
     .issuable-context-selectbox
       - if can?(current_user, :"admin_#{issuable.to_ability_name}", @project)
-        = f.select(:milestone_id, milestone_options(issuable), { include_blank: 'Select milestone' }, {class: 'select2 select2-compact js-select2 js-milestone'})
+        = f.select(:milestone_id, milestone_options(issuable), { include_blank: true }, { class: 'select2 select2-compact js-select2 js-milestone', data: { placeholder: 'Select milestone' }})
         = hidden_field_tag :issuable_context
         = f.submit class: 'btn hide'
 

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

@@ -39,9 +39,9 @@
         Assign to
       .col-sm-10
         = users_select_tag("#{issuable.class.model_name.param_key}[assignee_id]",
-            placeholder: 'Select a user', class: 'custom-form-control', null_user: true,
+            placeholder: 'Select assignee', class: 'custom-form-control', null_user: true,
             selected: issuable.assignee_id, project: @target_project || @project,
-            first_user: true, current_user: true)
+            first_user: true, current_user: true, include_blank: true)
          
         = link_to 'Assign to me', '#', class: 'btn assign-to-me-link'
   .form-group
@@ -52,7 +52,7 @@
       .col-sm-10
         - if milestone_options(issuable).present?
           = f.select(:milestone_id, milestone_options(issuable),
-            { include_blank: 'Select milestone' }, { class: 'select2' })
+            { include_blank: true }, { class: 'select2', data: { placeholder: 'Select milestone' } })
         - else
           .prepend-top-10
           %span.light No open milestones available.
@@ -66,7 +66,7 @@
     .col-sm-10
       - if issuable.project.labels.any?
         = f.collection_select :label_ids, issuable.project.labels.all, :id, :name,
-          { selected: issuable.label_ids }, multiple: true, class: 'select2'
+          { selected: issuable.label_ids }, multiple: true, class: 'select2', data: { placeholder: "Select labels" }
       - else
         .prepend-top-10
         %span.light No labels yet.
@@ -88,7 +88,7 @@
       %i.fa.fa-code-fork
       Target Branch
     .col-sm-10
-      = f.select(:target_branch, @merge_request.target_branches, { include_blank: "Select branch" }, { class: 'target_branch select2 span2', disabled: @merge_request.new_record? })
+      = f.select(:target_branch, @merge_request.target_branches, { include_blank: true }, { class: 'target_branch select2 span2', disabled: @merge_request.new_record?, data: {placeholder: "Select branch"} })
       - if @merge_request.new_record?
         %p.help-block
         = link_to 'Change branches', mr_change_branches_path(@merge_request)