code: public Data addAll(Iterable<Property> toAdd) {
          return !Iterables.isEmpty(toAdd)
                 ? new Data(Stream.concat(properties.stream(), StreamSupport.stream(toAdd.spliterator(), false)).collect(Collectors.toList()))
                 : this;
      }
docs: Adds properties to the data.
  
  @param toAdd the properties to add
  @return a new copy of the template.