Add not null constraint to run untagged runner option

db/migrate/20160504112519_add_run_untagged_to_ci_runner.rb

@@ -6,6 +6,6 @@ class AddRunUntaggedToCiRunner < ActiveRecord::Migration
   # caused by the default value.
   #
   def change
-    add_column :ci_runners, :run_untagged, :boolean, default: true
+    add_column :ci_runners, :run_untagged, :boolean, default: true, null: false
   end
 end

db/schema.rb

@@ -269,7 +269,7 @@ ActiveRecord::Schema.define(version: 20160509201028) do
     t.string   "revision"
     t.string   "platform"
     t.string   "architecture"
-    t.boolean  "run_untagged", default: true
+    t.boolean  "run_untagged", default: true,  null: false
   end
 
   add_index "ci_runners", ["description"], name: "index_ci_runners_on_description_trigram", using: :gin, opclasses: {"description"=>"gin_trgm_ops"}