Various fixes (#239)

* Handle Enumerables specifically

This avoids errors if the list is empty.

* Translation was missing, breaking click-testing in dev

* Conform to Linter and Styleguide

app/domain/export/tabular/messages/letters_with_invoice.rb

@@ -66,7 +66,15 @@ def message
     end
 
     def invoice_list
-      @invoice_list ||= list.first.first.invoice_list
+      @invoice_list ||= begin
+        if list.respond_to?(:peek)
+          list.peek
+        else
+          list.first
+        end.first.invoice_list
+      rescue StopIteration
+        nil
+      end
     end
   end
 end

config/locales/views.die_mitte.de.yml

@@ -21,3 +21,7 @@ de:
     address:
       two_with_same_last_name: '%{first} und %{second} %{last_name}'
   placeholder: Platzhalter
+
+  roles:
+    fields:
+      help_optional_label: Optionale Bezeichnung der Rolle dieser Person

lib/hitobito_die_mitte/wagon.rb

@@ -18,7 +18,6 @@ class Wagon < Rails::Engine
       #{config.root}/app/jobs ]
 
     config.to_prepare do
-      # rubocop:disable Metrics/LineLength
       # extend application classes here
       Group.include DieMitte::Group
       Role.include DieMitte::Role
@@ -57,7 +56,6 @@ class Wagon < Rails::Engine
 
       InvoiceItem.add_type_mapping(:variable_donation, InvoiceItem::VariableDonation)
       Role::Permissions << :complete_finance
-      # rubocop:enable Metrics/LineLength
     end
 
     initializer "die_mitte.add_settings" do |_app|