code: @Transactional
    public void populateLocalizationStrings(AllPropertiesMessageSource source) {
      source
          .getAllMessageIds()
          .asMap()
          .forEach(
              (namespace, messageIds) ->
                  updateNamespace(source, namespace, ImmutableSet.copyOf(messageIds)));
    }
docs: Adds all values in all namespaces from those specified in the property files for that
  namespace.
  
  <p>Already existing values are left exactly how they are. All new values are written to the
  repository.
  
  <p>If no {@link L10nString} exists yet for a certain messageID, a new one will be added.