default String renderComment(Generator gen, M model) {
        return model.getComment().map(comment -> 
            Stream.of(comment.split(Formatting.nl()))
                .map(row -> "// " + row)
                .collect(joining(Formatting.nl()))
        ).orElse("");
    }
Render the comment-part of the model, prepending each row with '//'.

@param gen    the generator
@param model  the model
@return       the generated code
common-parent/codegen/src/main/java/com/speedment/common/codegen/internal/java/view/trait/HasCommentView.java