Handle Route#name being nil after an update

It was possible for the `routes.name` field to be `NULL`, causing
`name_was` to be `nil` after a rename, resulting a bad first argument to
`sub` when attempting to rename descendants. This change adds a
condition to make sure `name_was` is present before attempting the
descendant update.

app/models/route.rb

@@ -21,7 +21,7 @@ class Route < ActiveRecord::Base
           attributes[:path] = route.path.sub(path_was, path)
         end
-        if name_changed? && route.name.present?
+        if name_changed? && name_was.present? && route.name.present?
           attributes[:name] = route.name.sub(name_was, name)
         end

spec/models/route_spec.rb

@@ -43,14 +43,22 @@ describe Route, models: true do
     end
     context 'name update' do
-      before { route.update_attributes(name: 'bar') }
-
       it "updates children routes with new path" do
+        route.update_attributes(name: 'bar') 
+
         expect(described_class.exists?(name: 'bar')).to be_truthy
         expect(described_class.exists?(name: 'bar / test')).to be_truthy
         expect(described_class.exists?(name: 'bar / test / foo')).to be_truthy
         expect(described_class.exists?(name: 'gitlab-org')).to be_truthy
       end
+
+      it 'handles a rename from nil' do
+        # Note: using `update_columns` to skip all validation and callbacks
+        route.update_columns(name: nil)
+
+        expect { route.update_attributes(name: 'bar') }
+          .to change { route.name }.from(nil).to('bar')
+      end
     end
   end
 end