Avoid showing label for unknown event type

app/decorators/event_decorator.rb

@@ -2,6 +2,7 @@
 
 EventDecorator = Struct.new(:event) do
   def event_type
+    return if event.event_type.blank?
     I18n.t("event_types.#{event.event_type}", app_name: APP_NAME)
   end
 

spec/decorators/event_decorator_spec.rb

@@ -5,6 +5,8 @@
   subject(:decorator) { EventDecorator.new(event) }
 
   describe '#event_type' do
+    subject(:event_type) { decorator.event_type }
+
     it 'returns the localized event_type' do
       expect(decorator.event_type).to eq t('event_types.email_changed')
     end
@@ -17,6 +19,18 @@
         expect(decorator.event_type).to include(APP_NAME)
       end
     end
+
+    context 'for a blank event type' do
+      # If the database has an event type value which isn't known to the application, it will be
+      # parsed as nil, which can result in unexpected behavior for retrieving a string label. This
+      # can happen during deployment of a new event type, where old servers aren't yet aware of the
+      # new event type, or it can happen if values are erroneously removed from the model enum while
+      # existing database records still use the value.
+
+      let(:event) { build_stubbed(:event, event_type: nil) }
+
+      it { is_expected.to be_nil }
+    end
   end
 
   describe '#last_sign_in_location_and_ip' do