Make it possible to set a site setting to empty string

app/controllers/admin/site_settings_controller.rb

@@ -7,7 +7,7 @@ class Admin::SiteSettingsController < Admin::AdminController
   end
 
   def update
-    params.require(:value)
+    raise ActionController::ParameterMissing.new(:value) unless params.has_key?(:value)
     SiteSetting.send("#{params[:id]}=", params[:value])
     render nothing: true
   end

spec/controllers/admin/site_settings_controller_spec.rb

@@ -34,10 +34,10 @@ describe Admin::SiteSettingsController do
         xhr :put, :update, id: 'test_setting', value: 'hello'
       end
 
-      # it 'allows value to be a blank string' do
-      #   SiteSetting.expects(:'test_setting=').with('').once
-      #   xhr :put, :update, id: 'test_setting', value: ''
-      # end
+      it 'allows value to be a blank string' do
+        SiteSetting.expects(:'test_setting=').with('').once
+        xhr :put, :update, id: 'test_setting', value: ''
+      end
     end
 
   end