Prefer attributes_for_keys so that it ignores nils

Also add a test for setting locked.

lib/ci/api/runners.rb

@@ -28,13 +28,9 @@ module Ci
         post "register" do
           required_attributes! [:token]
 
-          attributes = { description: params[:description],
-                         tag_list: params[:tag_list],
-                         locked: !!params[:locked] }
-
-          unless params[:run_untagged].nil?
-            attributes[:run_untagged] = params[:run_untagged]
-          end
+          attributes = attributes_for_keys(
+            [:description, :tag_list, :run_untagged, :locked]
+          )
 
           runner =
             if runner_registration_token_valid?

spec/requests/api/runners_spec.rb

@@ -187,14 +187,16 @@ describe API::Runners, api: true  do
           update_runner(shared_runner.id, admin, description: "#{description}_updated",
                                                  active: !active,
                                                  tag_list: ['ruby2.1', 'pgsql', 'mysql'],
-                                                 run_untagged: 'false')
+                                                 run_untagged: 'false',
+                                                 locked: 'true')
           shared_runner.reload
 
           expect(response.status).to eq(200)
           expect(shared_runner.description).to eq("#{description}_updated")
           expect(shared_runner.active).to eq(!active)
           expect(shared_runner.tag_list).to include('ruby2.1', 'pgsql', 'mysql')
-          expect(shared_runner.run_untagged?).to be false
+          expect(shared_runner.run_untagged?).to be(false)
+          expect(shared_runner.locked?).to be(true)
         end
       end