code: public static <M extends PMessage<M,F>, F extends PField, B extends PMessageBuilder<M,F>>
      List<M> buildAll(Collection<B> builders) {
          if (builders == null) {
              return null;
          }
          return builders.stream()
                         .map(PMessageBuilder::build)
                         .collect(Collectors.toList());
      }
docs: Build all items of the collection containing builders. The list must not
  contain any null items.
  
  @param builders List of builders.
  @param <M> The message type.
  @param <F> The field type.
  @param <B> The builder type.
  @return List of messages or null if null input.